Solution Design
Architecture that scales. We design multi-vendor network solutions — routed, switched, and overlay — aligned to your traffic patterns and business objectives.
Delivered at the Speed of Light
From carrier-grade telecommunications to AI-driven data fabrics — we architect, deploy, and automate the networks that power the largest leading enterprises.
Interconnected Systems Inc. is a premium provider of enterprise and telecom internetworking consulting and solutions. We have decades of experience, and our clients include some of the biggest names in media and telecommunications.
Our experts are certified in the latest technologies and well-versed in tackling any challenge — whether you need solution design, infrastructure assessment, full-scale implementation, or around-the-clock troubleshooting. We engineer networks that are resilient, automated, and ready for the demands of AI-era workloads.
Contact Us TodayFrom initial design through ongoing optimization — we deliver solutions at every stage of your network lifecycle.
Architecture that scales. We design multi-vendor network solutions — routed, switched, and overlay — aligned to your traffic patterns and business objectives.
Deep-dive audits of your existing environment. We identify performance bottlenecks, security gaps, and capacity constraints before they become outages.
Zero-downtime rollouts of complex network infrastructure. Certified engineers execute precision deployments across HPE, Juniper, and Cisco platforms.
Transform operations with intent-based networking and infrastructure-as-code. Reduce toil, eliminate config drift, and deploy changes in minutes with Ansible and Python.
Ultra-low-latency, high-throughput fabrics required for GPU clusters, ML training, and inference workloads. RDMA, RoCEv2, and lossless Ethernet expertise.
When the network is down, every second counts. Rapid root-cause analysis and resolution for the most complex multi-vendor, multi-protocol environments.
Deep, vendor-certified expertise across the industry's leading networking platforms — from physical transport to cloud overlay.
Deep, hands-on expertise across IOS-XE, IOS-XR, NX-OS, ACI, SD-WAN, and Catalyst. Routing, switching, security, wireless, and data center — certified and field-proven.
Junos OS experts delivering high-performance routing, switching, and security. Apstra-powered intent-based networking for modern AI-ready data centers.
HPE ProLiant, Synergy, and Aruba CX switching for AI-ready infrastructure. AOS-CX, ClearPass NAC, and Central cloud management.
Carrier-grade design and delivery. MPLS, BGP, optical transport, and last-mile connectivity for ISPs and large enterprise WAN environments.
Infrastructure-as-Code for networking. Ansible, Python, YANG, RESTCONF/NETCONF, and GitOps pipelines that eliminate manual toil at scale.
Purpose-built fabrics for GPU-dense AI/ML infrastructure. Lossless RoCEv2, ECN, PFC, and congestion control optimized for distributed training workloads.
AI infrastructure planning suite — LLM GPU & VRAM calculator, RoCEv2 fabric planner, inference serving simulator, vLLM/K8s config generator, TCO estimator, training storage sizer, and parallelism optimizer. Cloud Ops & multi-cloud networking — AWS/Azure/GCP interconnect & cost planner, VPC/VNet CIDR overlap detector, egress cost optimizer, PrivateLink/PSC sizing, hybrid connectivity comparator. Plus professional network tools: subnet calculator, BGP/ASN lookup, traceroute/MTR, DNS propagation, SPF/DMARC, VoIP, wireless calculators, and more. Free, no login required.
https://mcp.interconnectedsystems.net/mcp
No token · no sign-in · Streamable HTTP · 19 tools
All tools are open. An Authorization: Bearer header from an earlier setup is still accepted and can be left in place.
claude mcp add --transport http isi https://mcp.interconnectedsystems.net/mcp
Settings → Connectors → Add custom connector URL: https://mcp.interconnectedsystems.net/mcp Authentication: None
{"mcpServers":{"isi":{"type":"http","url":"https://mcp.interconnectedsystems.net/mcp"}}}
Identify the manufacturer of any network device from its MAC address using the full IEEE OUI registry (MA-L, MA-M, MA-S — 52,000+ entries, hosted locally).
Detect your public IPv4 and IPv6 addresses as seen from the internet.
Look up geolocation, ISP, ASN, and timezone for any IP address. Leave blank to look up your own IP.
Trace the IPv4 or IPv6 network path from our server to any host — shows each hop, packet loss, and average latency. Full mode runs the trace for ~2 minutes with live-updating Sent / Received / Loss / Best / Avg / Worst / StDev statistics, just like running mtr in a terminal.
Deep network path analysis with automatic MPLS label-stack decoding, ECMP/load-balancing path discovery, NAT identification, Path MTU, and ASN/geo enrichment per hop. Multi-protocol: ICMP, UDP, or TCP.
TCP connect scan from our server against any public host. Private IPs blocked. Max 20 ports, 30-second rate limit per IP. Custom: enter ports as 80,443,8000-8010.
| Protocol | Header (bytes) | Notes |
|---|---|---|
| Ethernet II | 14 | 6 dst + 6 src + 2 EtherType |
| 802.1Q VLAN | +4 | TPID(2) + TCI(2) inserted |
| 802.1ad Q-in-Q | +8 | Outer + inner VLAN tags |
| IPv4 | 20 – 60 | 20 min; options add up to 40 |
| IPv6 | 40 | Fixed; ext. headers are separate |
| TCP | 20 – 60 | 20 min; options (SACK, TS) up to 40 |
| UDP | 8 | Fixed; src/dst port + len + checksum |
| ICMP / ICMPv6 | 8 | Echo: type+code+checksum+id+seq |
| MPLS label | 4 / label | Label(20b)+TC(3)+S(1)+TTL(8) |
| GRE | 4 – 16 | 4 min; +4 each for key/seq/checksum |
| VXLAN | 8 | +outer UDP(8)+IP(20)+Eth(14) = 50 total |
| GENEVE | 8+ | 8 fixed + variable TLV options |
| GTP-U | 8 – 12 | LTE/5G user plane; 8 min |
| IPsec ESP | 8+ | SPI(4)+Seq(4)+IV+payload+ICV |
| IPsec AH | 24 | Fixed for SHA-256; no encryption |
| NSH | 8+ | Network Svc Header (SFC path) |
| SRv6 SRH | 8+(16×n) | 8 base + 16 bytes per SID in list |
| PPPoE | +8 | Over Ethernet; adds 6-byte hdr + 2 proto |
Tests the connection from our server in Toronto, ON to your browser — measured independently over IPv4 and IPv6. Reports scored quality (0–100) with latency, jitter, throughput, and UDP reachability, plus a live map showing the path and approximate distance.
| CIDR | Subnet Mask | Hosts |
|---|
Theoretical network limit via the Mathis formula: T = (MSS / RTT) × (1 / √Loss). Enter MSS, RTT, and observed loss rate to find the maximum achievable TCP throughput.
Bandwidth-Delay Product & TCP buffer sizing: BDP = BW × RTT, T ≤ buffer / RTT. Shows how much window you need and what throughput your current buffer actually delivers.
Checks an IPv4 against GreyNoise, FireHOL Level 1 (Spamhaus DROP + DShield + Feodo), OTX AlienVault, Emerging Threats, and 17 DNS blacklists in parallel. Links to Cisco Talos Intelligence for full analysis.
Checks a URL or domain against OpenPhish (active phishing feed), GreyNoise, FireHOL Level 1, and 6 DNS blacklists on the resolved IP. Links to Cisco Talos and VirusTotal for deeper analysis.
Official validated design guides and reference architectures for AI GPU cluster networking. Click any document to open it in a new tab.
Visual comparison of three GPU cluster fabric architectures based on the Juniper JVD "Glittery Dawn" AI Data Center validated design and NVIDIA DGX SuperPOD reference. Shows rail-optimized (1 leaf per GPU rail), NVIDIA SuperPOD / GB200 NVL72, and standard fat-tree — with colored topology diagrams, PXN / NVLink annotations, and a side-by-side metric breakdown.
Estimate VRAM requirements, KV cache, and maximum concurrent users for self-hosted LLM inference. Supports Llama, Qwen (including 3.8 27B), DeepSeek, Mistral, Gemma 4, gpt-oss, Kimi, GLM, Phi, and custom architectures. Multi-GPU tensor parallel and interconnect guidance included.
Size and validate a production-grade RoCEv2 Ethernet fabric for GPU training and inference clusters. Models four parallelism strategies (Data / Tensor / Pipeline / Hybrid) — each with correct collective formulas, ring sizes, and fabric-score penalties. Uses the Juniper JVD stripe model for accurate leaf counts in rail-optimized designs. Outputs a full switch BOM with part numbers and cable estimates, 2-tier or 3-tier Clos (Superspine) topology diagrams, AllReduce / P2P transfer time, BDP / PFC / ECN thresholds, vendor config snippets, and a comprehensive CSV export. Includes RoCEv2 vs InfiniBand comparison.
Calculate per-rack and cluster power draw (kW), cooling load (BTU / tons), PDU/UPS sizing, rack layout, and monthly OpEx for GPU clusters. Includes RoCE switch and NIC power — a cost factor most vendor tools omit. Chains from the Fabric Planner above.
Spreadsheet-style 3–5 year Total Cost of Ownership: CapEx breakdown, annual OpEx, break-even vs cloud GPU rental, and cumulative cost chart. Hardware costs pre-filled with 2025–2026 market pricing — edit any field to match your actual quotes.
Size NVMe/Ceph storage and I/O for LLM training. Computes dataset storage (with correct uint16/uint32 token precision for your vocabulary size), checkpoint size at 14 bytes/param (BF16 weights + FP32 master copy + Adam m+v — the full mixed-precision footprint), per-node ZeRO-3 checkpoint shards, data-loading I/O (correctly low — transformer LLMs are compute-bound, not I/O-bound), checkpoint burst bandwidth as the real storage sizing driver, and Ceph write-amplified east-west fabric impact. Filesystem tier recommendation is driven by checkpoint burst, not data-loading I/O. Ceph selected: shows OSD count, OSD server count, per-server RAM, and NIC sizing.
Recommends the optimal Data / Tensor / Pipeline parallelism mix and ZeRO stage for your model and cluster. Uses exact ZeRO memory formulas from Rajbhandari et al. (SC'20): ZeRO-0 = 16Ψ, ZeRO-1 = 4Ψ + 12Ψ/Nd, ZeRO-3 = 16Ψ/Nd bytes per GPU. TFLOPS are dense BF16 (training uses dense arithmetic, not sparse). Activation memory is parameterized by sequence length. Pipeline bubble uses correct micro-batch count from seq_len. ZeRO-3 AllReduce overhead includes the 1.5× communication factor from the forward-pass AllGather. Directly informs 2-tier vs 3-tier fabric choice.
Simulate production LLM serving performance: TTFT, decode throughput, p95 latency, and max QPS for vLLM, TGI, Ollama, and TensorRT-LLM. Models continuous batching, paged-attention KV cache capacity, and multi-GPU tensor-parallel AllReduce east-west bandwidth.
Generate ready-to-copy deployment configs from your model and serving parameters: docker run, docker-compose.yaml, Kubernetes manifests, Helm values, and NCCL/RoCEv2 env vars. Full-deployment mode adds inline comments and production hardening; Skeleton outputs minimal working configs. Import directly from the Serving Simulator above.
Live operational status for 21 cloud, AI, and networking providers — including Anthropic (Claude), OpenAI, Cohere, Together AI, Fireworks AI, Replit, Cerebras, and BaseTen. Data is fetched server-side and cached for 90 seconds.
Enter an AS number to retrieve BGP origin info, name, registry, country, and announced prefixes.
Look up BGP routing info for any IPv4 or IPv6 prefix — origin ASN, announcing organization, and upstream visibility.
Enter any IP address to find its origin ASN, announced prefix, registry info, and geolocation.
Interactive BGP terminal connected directly to public Route Views servers. Type Cisco IOS commands — try show ip bgp summary or show ip bgp 8.8.8.0/24. Read-only; no authentication required.
Public BGP looking glasses — run traceroute, ping, and BGP table queries from global vantage points.
Query any DNS record type via a public resolver of your choice. Select a DNS server from around the world to see what it returns.
Resolve an IP address to its hostname via PTR record lookup. Works for both IPv4 and IPv6 addresses. Choose a DNS server to query.
Compare DNS responses from Google (8.8.8.8) and Cloudflare (1.1.1.1) to verify a record has propagated globally.
Check a domain's email authentication setup — MX mail servers, SPF sender policy, and DMARC enforcement policy.
Check whether a domain has DNSSEC enabled and whether its signatures validate correctly via Google's validating resolver.
Check an IPv4 address against 17 validated DNS blacklists (DNSBLs) in parallel. All sources verified for correct NXDOMAIN / A-record behaviour. Results in ~5 seconds.
Check syntax, MX records, SPF, DMARC, disposable domain detection, MX server reputation, and SMTP deliverability — all in one check. Results in ~5–10 seconds.
EHLO and RCPT TO, then immediately disconnects. This leaves a single line in the target server's connection log.Read-only reporting for Juniper Mist and SSR, gathered into one browser extension. Pick a region, paste an Observer API token, choose a tool and press Run: the result previews on screen and lands as a styled .xlsx in your downloads. Everything runs in the browser — no Python, no server, no telemetry, not one third-party dependency.
set commands, one .zip with a folder per siteThe 13 built-in tools are a starting point. A tool is one JavaScript file; the toolbox supplies the menu card, token and org handling, the site picker, the settings form, progress, preview and the .xlsx. The extension ships its own LLM spec, TOOL_PROMPT.md — press Manage tools → Copy AI prompt, paste it into Claude, ChatGPT, Copilot or Gemini, then paste a Python or Node script you already have, or just describe the report you want.
your script or idea + TOOL_PROMPT.md → AI assistant → my-report.js → Manage tools → Install → new tool card
The returned file is checked before anything is written: Node or Python code, raw fetch, storage, console.*, POSTs and npm imports are refused with an explanation of what to fix. Once it passes, it is written into the extension’s tools/ folder and its card appears without a reload, so your token survives — with a Remove button beside it. The check catches mistakes, not malice: install tools only from people you trust.
The token lives in memory in that one tab — never written to storage, never sent to the service worker, never logged — and is wiped after 30 idle minutes or when the tab closes. Nothing issues a write to Mist. 13 pinned Mist API hosts and no permissions entries; the SSR Conductor origin is asked for once, at runtime, the first time you connect.
Every tool
The Excel workbooks they save
Add your own tool
chrome://extensions
Unzip the download somewhere permanent. Browsers refuse links to chrome://, so paste that URL into the address bar. Turn on Developer mode, click Load unpacked, and select the unzipped mist-toolbox folder — the one containing manifest.json. Pin the icon.
edge://extensions
The same package; Chrome or Edge 116 and later. Turn on Developer mode, choose Load unpacked, and pick the same folder. Not Safari.
Toolbar icon the toolbox opens in one reused tab Region your Mist cloud, e.g. api.gc2.mist.com Token My Account → API Tokens (Observer is enough) Run pick an org and a tool → .xlsx download
The on-screen table previews up to 200 rows; the spreadsheet always has everything. SSR Pre/Post Check asks for its own Conductor URL and credentials.
Manage tools → Copy AI prompt paste into any AI assistant + your script or idea Manage tools → choose the .js it returns → Install
The first install in a tab asks you to pick the mist-toolbox folder and allow the browser to edit it. That needs an unpacked install — a packed copy can’t be written to.
unzip the new release over the mist-toolbox folder then press reload on the extension’s card
Tools you added live in tools/ — back them up first if you replace the whole folder. The SHA-256 of each mist-toolbox.zip is on its GitHub release page.
git clone https://github.com/InterconnectedSystems/mist-toolbox cd mist-toolbox/mist-toolbox node --test tests/
225 tests, plain node --test, no dependencies. The suite checks every tool against the scripts it was ported from, and the tool checker and token policy. Tests are not in the release zip.
Convert between dBm, dBW, mW, W, and µW. Essential for reading RF specs and regulatory limits.
Calculate signal attenuation over distance using the Friis transmission equation. Ideal conditions, no obstacles.
Effective Isotropic Radiated Power — Tx Power + Antenna Gain − Cable Loss. Used for regulatory compliance.
Calculate received signal power and link margin for a point-to-point wireless link.
Translate a received signal level (dBm) into quality rating, estimated SNR, and expected 802.11ax throughput.
| Ch | Center (MHz) | Notes |
|---|
Calculate bandwidth per call including RTP/UDP/IP and Ethernet overhead for common VoIP codecs.
How many concurrent VoIP calls fit in a given link bandwidth? Results shown per codec (full-duplex, with Ethernet overhead).
Estimate MOS (1–5) and R-Factor using the ITU-T E-Model. Accounts for codec, one-way delay, packet loss, and jitter.
Click keys to generate DTMF tones via the Web Audio API. Plays dual-tone multi-frequency signals used in telephony.
Look up SIP SRV records (_sip._udp, _sip._tcp, _sips._tcp) to find SIP server addresses and ports for a domain.
| Code | Description |
|---|
CISA Known Exploited Vulnerabilities (actively exploited in the wild) + NIST NVD CRITICAL & HIGH CVEs from the last 14 days. Updated daily. CISA KEV catalog ↗
Full feed
Daily operator brief of new IETF RFCs, in-scope Internet-Drafts, and protocol-registry movement — networking, routing, ops, transport, VoIP/IMS, and protocol security. Analysed with Grok 4.7. RFC Editor ↗ · Datatracker ↗
Every cost calculation in this tab uses rates from the official cloud provider pricing APIs, refreshed daily. The full pricing dataset is published as a static JSON file so you can audit every number used — no hidden multipliers or undocumented assumptions.
Select source and destination cloud regions or on-premises, define bandwidth and latency requirements, and compare all connectivity options — VPN, Direct Connect/ExpressRoute/Cloud Interconnect, PrivateLink/PSC, Transit Gateway/Virtual WAN/NCC, and SD-WAN — with monthly cost estimates, latency ranges, setup timelines, and a recommendation.
Defaults assume constant 24/7 outbound traffic. If your monitoring shows a different pattern, dial it in here for a more accurate BOM.
Detect overlapping CIDR blocks across VPCs, VNets, and VCNs — or auto-allocate non-overlapping subnets for a multi-cloud environment. Applies cloud-specific reserved IP rules: AWS reserves 5 IPs per subnet (.0 network, .1 router, .2 DNS, .3 future use, .255 broadcast); Azure reserves 5 (.0 network, .1 gateway, .2–.3 DNS, .255 broadcast); GCP reserves 2 (.0 network, .255 broadcast).
Enter any mix of IPv4 CIDRs. Results show pairwise overlap detection and the usable host count per subnet after cloud-specific IP reservations.
Drag the sliders to define monthly traffic volumes across four cost categories. Compare total egress spend across AWS, Azure, and GCP with tiered pricing applied. Get actionable tips to reduce spend via PrivateLink, CDN placement, or traffic routing changes.
Estimate monthly costs for AWS PrivateLink, Azure Private Endpoints, or GCP Private Service Connect. Model endpoint hours, data processing charges, and compare against public API egress costs. Includes auto-scaling guidance based on concurrent connection load.
Define your on-premises location, target cloud, bandwidth requirements, latency SLA, and compliance needs. Get a side-by-side comparison of all hybrid connectivity options — IPsec VPN, dedicated circuits (Direct Connect / ExpressRoute / Cloud Interconnect), PrivateLink/PSC, Transit Gateway, and SD-WAN — with monthly costs, failure modes, and a scored recommendation.
Paste rules from AWS describe-security-groups, Azure az network nsg show, or GCP gcloud firewall-rules list — or build them in the table editor. Detects shadow rules (Azure/GCP first-match-wins), redundant rules (AWS), overly permissive entries (sensitive ports exposed publicly), and least-privilege gaps. Includes a what-if traffic tester that walks the ruleset to predict allow/deny verdicts.
Generate validated Terraform, CloudFormation, or Bicep snippets for common multi-cloud networking patterns — VPCs/VNets, subnets, security groups/NSGs/firewalls, peering, Transit Gateway/Virtual WAN, PrivateLink/PSC, and more. Each snippet is parameterized; outputs are checked for required fields, CIDR validity, CIDR overlap (subnet within VPC), and basic syntax balance. Copy or download as a ready-to-apply file.
Cisco & Arista use Administrative Distance (0–255). Juniper uses Route Preference (same semantics, wider scale). Lower value wins on all platforms.
| Protocol / Source | Cisco IOS/XE/XR | Juniper Junos | Arista EOS |
|---|---|---|---|
| Connected | 0 | 0 | 0 |
| Static | 1 | 5 | 1 |
| EIGRP Summary | 5 | — | — |
| EIGRP Internal | 90 | — | — |
| OSPF Internal | 110 | 10 | 110 |
| IS-IS L1 Internal | 115 | 15 | 115 |
| IS-IS L2 Internal | 115 | 18 | 115 |
| RIP | 120 | 100 | 120 |
| OSPF External | 110 | 150 | 110 |
| IS-IS L1 External | 115 | 160 | — |
| IS-IS L2 External | 115 | 165 | — |
| EIGRP External | 170 | — | — |
| iBGP | 200 | 170 | 200 |
| eBGP | 20 | 170 | 200 ¹ |
¹ Arista defaults eBGP and iBGP both to AD 200. Use distance bgp 20 200 200 for Cisco-parity. Junos uses the same preference (170) for both iBGP and eBGP. EIGRP is Cisco-only.
LSA Types
| Type | Name | Scope |
|---|---|---|
| 1 | Router LSA | Intra-area |
| 2 | Network LSA (DR) | Intra-area |
| 3 | Summary Network LSA (ABR) | Inter-area |
| 4 | ASBR Summary LSA (ABR) | Inter-area |
| 5 | AS External LSA (ASBR) | AS-wide |
| 7 | NSSA External LSA | NSSA area |
| 9 | Opaque (link-local, TE, SR) | Link-local |
| 10 | Opaque (area, TE RSVP) | Intra-area |
| 11 | Opaque (AS-wide) | AS-wide |
Neighbor States
Down → Attempt → Init → 2-Way → ExStart → Exchange → Loading → Full
Area Types
| Area | LSA 5 | LSA 3/4 | LSA 7 |
|---|---|---|---|
| Backbone (0) | ✓ | ✓ | ✗ |
| Stub | ✗ | ✓ | ✗ |
| Totally Stub | ✗ | ✗ (default only) | ✗ |
| NSSA | ✗ | ✓ | ✓ |
| Totally NSSA | ✗ | ✗ | ✓ |
Key timers: Hello 10 s / Dead 40 s (NBMA: 30/120). LSA max-age 3600 s. DR/BDR elected on broadcast & NBMA only.
Vendor Differences
| Reference BW | Default 100 Mbps on all three. Tune with auto-cost reference-bandwidth (Cisco/Arista) or reference-bandwidth (Junos). |
| Dead/Hello sync | Arista: dead-interval is not auto-adjusted when hello-interval changes — set both manually. Cisco & Junos auto-derive dead = hello × 4. |
| GR helper mode | Juniper: enabled by default (RFC 3623). Cisco & Arista: require explicit configuration. |
| External routes | E2 is default on all three. E1 cost = redistributed metric + cost to ASBR. When both E1 and E2 exist for same prefix, E1 is always preferred. |
| Property | iBGP | eBGP |
|---|---|---|
| AD | 200 | 20 |
| NEXT_HOP | Unchanged | Set to self |
| AS_PATH | Unchanged | Prepend own ASN |
| LOCAL_PREF | Propagated | Not sent out |
| MED | Not propagated | Sent to eBGP peer |
| Full mesh | Required (or RR/Confed) | N/A |
| TTL | 255 | 1 (use EBGP multihop) |
Path Selection (in order)
| 1 | Highest WEIGHT (Cisco-local) |
| 2 | Highest LOCAL_PREF |
| 3 | Locally originated (network/aggregate) |
| 4 | Shortest AS_PATH |
| 5 | Lowest ORIGIN (IGP < EGP < Incomplete) |
| 6 | Lowest MED (same AS) |
| 7 | Prefer eBGP over iBGP |
| 8 | Lowest IGP metric to NEXT_HOP |
| 9 | Oldest eBGP path / lowest Router ID |
| 10 | Lowest peer IP address |
Path Selection — Vendor Differences
| Cisco IOS/XE/XR | Step 1 is WEIGHT (local, not advertised; default 0 learned / 32768 local). Remaining steps as listed above. |
| Juniper Junos | No WEIGHT — selection begins at LOCAL_PREF. Next-hop must be resolvable (implicit prereq). Final tiebreaker: lowest router ID. |
| Arista EOS | WEIGHT supported (Cisco-compatible step 1). Final tiebreaker: lowest peer IP address. |
Tune with bgp bestpath knobs (Cisco/Arista) or set protocols bgp path-selection (Junos).
Levels
| Level | Function | LSDB |
|---|---|---|
| L1 | Intra-area routing | Area LSDB |
| L2 | Inter-area (backbone) | Backbone LSDB |
| L1/L2 | ABR equivalent | Both LSDBs |
PDU Types
| PDU | Purpose |
|---|---|
| IIH | IS-IS Hello — neighbour discovery & keepalive |
| LSP | Link State PDU — topology advertisement |
| CSNP | Complete Seq. — full LSDB summary (DR only) |
| PSNP | Partial Seq. — request / acknowledge LSPs |
Key TLVs
| TLV | Description |
|---|---|
| 1 | Area Addresses |
| 2 | IS Neighbours (L1) |
| 22 | Extended IS Reachability (TE metric) |
| 128 | IP Internal Reachability |
| 130 | IP External Reachability |
| 135 | Extended IP Reachability (TE) |
| 232 | IPv6 Reachability |
| 236 | IPv6 Interface Address |
NET format: 49.0001.0100.1001.0001.00 — Area · System-ID · NSEL(00)
Vendor Differences
| Metric style | Cisco: narrow default — add metric-style wide for TE/SR. Juniper: advertises both narrow + wide by default. Arista: narrow default. |
| DIS hello timers | Juniper: DIS hello 3 s / hold 9 s (÷3 from standard 9 s/27 s). Cisco: does not auto-scale DIS hellos. |
| Interface default metric | 10 on all three platforms. |
Label Operations
| Op | Description |
|---|---|
| PUSH | Add label (ingress LER) |
| SWAP | Replace label (transit LSR) |
| POP | Remove label (egress LER) |
| PHP | Pop one hop before egress. The egress signals label 3 (implicit null) |
Label Stack Entry (32 bits)
Label (20b) · TC/EXP (3b, QoS) · S bit (1b, bottom-of-stack) · TTL (8b). 4 bytes per label.
Special-Purpose Labels (0–15)
| Label | Meaning |
|---|---|
| 0 | IPv4 Explicit NULL. Keeps TC bits to the egress |
| 1 | Router Alert |
| 2 | IPv6 Explicit NULL |
| 3 | Implicit NULL. Signalled only, never on the wire |
| 4 | MPLS Network Actions (MNA), RFC 9994 |
| 7 | Entropy Label Indicator (ELI), RFC 6790 |
| 13 | Generic Associated Channel Label (GAL) |
| 14 | OAM Alert |
| 15 | Extension Label (XL). Next label is an extended special-purpose value |
Labels 5, 6 and 8–12 are unassigned. Ordinary labels start at 16.
Entropy Label
Ingress pushes ELI (7) + EL, 8 bytes. Transit LSRs hash on the EL for ECMP without parsing the payload. The egress advertises Entropy Label Capability (ELC). Each LSR advertises its Entropy Readable Label Depth (ERLD), which limits how deep the ELI/EL pair may sit in an SR label stack (RFC 8662).
MPLS Network Actions (MNA)
New in 2025–2026. A sub-stack that starts with label 4 carries network actions and their data inside the label stack (framework RFC 9789, encoding RFC 9994, June 2026). Use cases are in RFC 9791. Carrying data after the stack (post-stack header) is still an Internet-Draft: draft-ietf-mpls-mna-ps-hdr-19, in the RFC Editor queue as of Nov 2026.
SID Types
| SID | Description |
|---|---|
| Prefix-SID | Global. An index into the SRGB: label = SRGB base + index |
| Node-SID | Prefix-SID on a node loopback (N flag set) |
| Anycast-SID | Same Prefix-SID advertised by several nodes |
| Adj-SID | Local to one node. One per adjacency, dynamic or from the SRLB |
| Binding SID | Local label that steers into an SR Policy |
| BGP Prefix-SID | Prefix-SID carried in BGP labeled unicast (RFC 8669) |
| Flex-Algo SID | Extra Prefix-SID per algorithm 128–255 (RFC 9350) |
Algorithm 0 = SPF, 1 = strict SPF, 128–255 = operator-defined Flex-Algo (metric type + constraints).
Blocks and Limits
| SRGB | Global block for Prefix-SIDs. Use the same range on every node |
| SRLB | Local block for Adj-SIDs and other local SIDs |
| MSD | Maximum SID Depth a node can push. Advertised in IS-IS (RFC 8491) and OSPF (RFC 8476) |
| P / E flags | P = no PHP. E = replace with explicit null |
SR Policy (RFC 9256)
Identified by (headend, color, endpoint). Holds candidate paths ranked by preference; each has one or more weighted segment lists. A Binding SID represents the policy. Signalled by BGP (RFC 9830), PCEP (RFC 8664) or local config. Service routes steer in by matching the BGP color community.
Fast Reroute
TI-LFA (RFC 9855, Oct 2025): the backup follows the post-convergence path, encoded as a short repair segment list. Covers link, node and SRLG failures in any topology.
Vendor Differences
| SRGB (Cisco) | 16000–23999 default. Configure with segment-routing global-block. |
| SRGB (Juniper) | No fixed default. Taken from the dynamic label pool, so set srgb start-label explicitly. |
| SRGB (Arista) | 900000–965535 default. Configure with segment-routing global-block. |
| TI-LFA | Cisco: IS-IS and OSPF. Juniper: IS-IS and OSPFv2. Arista: IS-IS documented; check release notes for OSPF. |
With different SRGBs per vendor, the same index gives a different label on each node. Align the SRGB everywhere, or plan SIDs as indexes, never as absolute labels.
SID Structure
An SRv6 SID is an IPv6 address: Locator : Function : Argument, 128 bits in total. The locator is Block : Node and is advertised as an ordinary IPv6 prefix, so nodes that are not segment endpoints only need plain IPv6 forwarding.
Segment Routing Header (RFC 8754)
IPv6 Routing header type 4. 8 bytes fixed + 16 bytes per SID. The segment list is stored in reverse order; Segments Left points at the active SID, which is also the IPv6 destination address.
Endpoint Behaviours (RFC 8986)
| Behaviour | Description |
|---|---|
| End | Node segment. SRv6 form of a Prefix-SID |
| End.X | L3 cross-connect to one adjacency. SRv6 form of an Adj-SID |
| End.T | Lookup in a specific IPv6 table |
| End.DT4 / DT6 / DT46 | Decapsulate, then look up in a VRF table (per-VRF L3VPN) |
| End.DX4 / DX6 | Decapsulate, then cross-connect to a CE adjacency (per-CE L3VPN) |
| End.DX2 | Decapsulate, then send the Ethernet frame out an interface (EVPN VPWS) |
| End.DT2U / DT2M | Decapsulate, then bridge: unicast MAC lookup / BUM flood (EVPN) |
| End.B6.Encaps | Binding SID into an SRv6 Policy |
| End.BM | Binding SID into an SR-MPLS Policy |
Flavors and Headend
| PSP | Penultimate Segment Pop. SRH removed one segment early |
| USP | Ultimate Segment Pop. SRH removed at the last segment |
| USD | Ultimate Segment Decapsulation. Outer IPv6 header removed at the last segment |
| H.Encaps | Headend adds an outer IPv6 header + SRH |
| H.Encaps.Red | Same, but the first SID is only in the destination address. With one segment the SRH can be left out |
uSID / Compressed SID (RFC 9800, June 2025)
| NEXT-CSID | The uSID flavor. Several short SIDs packed into one 128-bit container |
| F3216 | 32-bit Locator-Block + 16-bit uSIDs. The format every NEXT-CSID implementation must support |
| Capacity | (128 − 32) / 16 = 6 uSIDs per container |
| Forwarding | The node that owns the first uSID shifts the rest left by 16 bits, zero-fills the end, and forwards on the new destination address |
| GIB / LIB | Global ID Block for domain-wide uSIDs (nodes). Local ID Block for per-node uSIDs (adjacencies, services). The split is a deployment choice |
| REPLACE-CSID | The other RFC 9800 flavor. 32-bit CSIDs packed in the SRH replace part of the destination address at each hop |
Example with block 2001:db8::/32: 2001:db8:100:200:300:: → node 0100 → 2001:db8:200:300:: → node 0200 → 2001:db8:300::. Three segments, no SRH.
Vendor shorthand, not RFC terms: uN = End with NEXT-CSID · uA = End.X with NEXT-CSID · uDT4 / uDT6 / uDT46 = End.DT4 / DT6 / DT46 · uDX2 = End.DX2. Decapsulation SIDs sit last in the list, so they need no NEXT-CSID flavor.
Addressing and Control Plane
IANA assigned 5f00::/16 for SRv6 SIDs (RFC 9602); it is not globally reachable and is easy to filter at the domain edge. Locators are flooded by IS-IS (RFC 9352) or OSPFv3 (RFC 9513). VPN and EVPN service SIDs are carried in BGP (RFC 9252). Ping and traceroute to SIDs: RFC 9259.
| Property | SR-MPLS | SRv6 (full SID) | SRv6 uSID |
|---|---|---|---|
| Data plane | MPLS label stack | IPv6 + SRH | IPv6. SRH only beyond 6 uSIDs |
| Segment size | 4 bytes | 16 bytes | 2 bytes (F3216) |
| 1 segment | 4 B | 40 B | 40 B |
| 5 segments | 20 B | 112 B | 40 B |
| 10 segments | 40 B | 192 B | 64 B |
| Transit nodes | Must forward MPLS | Plain IPv6 is enough | Plain IPv6 is enough |
| ECMP entropy | Entropy label (+8 B) | IPv6 flow label | IPv6 flow label |
| Summarization | No. One label per prefix | Yes. Locators aggregate | Yes. Locators aggregate |
| Service demux | VPN label | End.DT / End.DX SID | Service uSID, last in list |
| Fast reroute | TI-LFA | TI-LFA | TI-LFA |
Overhead is the added encapsulation with reduced encapsulation (H.Encaps.Red): 40 B outer IPv6 header, plus an SRH of 8 B + 16 B per remaining SID or uSID container. Count the service SID as a segment. Budget MTU for it on every core link.
Interworking between SRv6 and MPLS domains is still an Internet-Draft: draft-ietf-spring-srv6-mpls-interworking-03 (Aug 2026).
Standards Map (checked Nov 2026)
| Document | Subject |
|---|---|
| RFC 8402 | Segment Routing architecture |
| RFC 8660 | SR with the MPLS data plane |
| RFC 8754 | IPv6 Segment Routing Header |
| RFC 8986 | SRv6 network programming (behaviours) |
| RFC 9252 | BGP VPN and EVPN services over SRv6 |
| RFC 9256 | SR Policy architecture |
| RFC 9350 | IGP Flexible Algorithm |
| RFC 9602 | SRv6 SID address block 5f00::/16 |
| RFC 9800 | Compressed SRv6 segment lists (uSID), June 2025 |
| RFC 9830 | SR Policies in BGP, Sept 2025 |
| RFC 9855 | TI-LFA, Oct 2025 |
| RFC 9871 | BGP Color-Aware Routing (Experimental), Nov 2025 |
| RFC 9832 | BGP Classful Transport (Experimental), Sept 2025 |
| RFC 9994 | MPLS Network Actions sub-stack, June 2026 |
| srv6-security-19 | Draft. SRv6 security considerations. RFC Editor queue |
| srv6addressing-01 | Draft. SRv6 addressing recommendations |
Drafts change and can expire. The RFC Brief tab tracks new SPRING, MPLS and SRv6 documents daily.
| Type | Name | Purpose |
|---|---|---|
| 1 | Ethernet Auto-Discovery | Mass withdrawal, aliasing (multi-homing) |
| 2 | MAC/IP Advertisement | MAC learning, ARP suppression, host routes |
| 3 | Inclusive Multicast ET (IMET) | BUM flooding — announce VTEP membership |
| 4 | Ethernet Segment Route | DF election, multi-homing ES discovery |
| 5 | IP Prefix Route | IRB/inter-subnet routing, L3VPN prefixes |
VXLAN Concepts
| Term | Detail |
|---|---|
| VNI | 24-bit VXLAN Network ID (~16M segments) |
| UDP port | 4789 (IANA) — outer UDP encapsulation |
| VTEP | VXLAN Tunnel Endpoint — encap/decap point |
| L2 VNI | Bridge domain / broadcast domain |
| L3 VNI | VRF / inter-subnet routing (symmetric IRB) |
IRB Models
| Model | Route at | L3 VNI |
|---|---|---|
| Asymmetric | Ingress only | Not required |
| Symmetric | Ingress + Egress | Required (per VRF) |
RT format: ASN:VNI. BGP EVPN AFI 25/SAFI 70. Type-2 carries MAC+IP, enables ARP suppression. Type-5 enables host-route injection from VMs.
| Attribute | Type | Scope |
|---|---|---|
| ORIGIN | Well-known mandatory | IGP / EGP / incomplete |
| AS_PATH | Well-known mandatory | Loop prevention + path selection |
| NEXT_HOP | Well-known mandatory | Next-hop IP for prefix |
| LOCAL_PREF | Well-known discretionary | iBGP only — exit selection |
| ATOMIC_AGGR | Well-known discretionary | Aggregation indicator |
| MED | Optional non-transitive | Suggest entry point to neighbour AS |
| COMMUNITY | Optional transitive | 32-bit tag — policy signalling |
| EXT_COMMUNITY | Optional transitive | 64-bit — VPN RT/RD, SoO, CoS |
| LARGE_COMMUNITY | Optional transitive | 96-bit — RFC 8092 |
| AGGREGATOR | Optional transitive | ASN + IP of aggregating router |
Well-known Communities
| Value | Meaning |
|---|---|
| NO_EXPORT (0xFFFFFF01) | Do not advertise beyond AS boundary |
| NO_ADVERTISE (0xFFFFFF02) | Do not advertise to any peer |
| NO_EXPORT_SUBCONFED (0xFFFFFF03) | Do not export to eBGP sub-confederation peers |
| BLACKHOLE (65535:666) | RTBH — discard matching traffic (RFC 7999) |
Common BFD Timers (reference)
Min interval 50–300 ms typical. Multiplier 3 (detect = interval × mult). Async mode standard; Echo mode for single-hop. Micro BFD for LAG members.
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