FOUNDRYNETNo. 001SEPTEMBER 2026SECTION 03ROUTING
Network Routing Guide
Four guides on moving packets between networks and keeping the path up when a router fails. The section inherits the NetIron documentation and the most-searched query on the original site, which was simply ipv6.
03 Contents
- VRRP and VSRP: First-Hop Redundancy ExplainedGuide
VRRP lets two or more routers share one gateway address so hosts keep a working default route when a router dies. Foundry extended it as VRRP-E and built VSRP to protect Layer 2 uplinks the same way.
- MPLS VPN: Labels, LSPs, Layer 3 and Layer 2 VPNsGuide
MPLS forwards packets on short labels instead of IP lookups, and MPLS VPNs use those labels to carry many customers over one provider core while keeping their routing tables apart.
- IPv6 Transition: Dual Stack, Tunnels, Translation and PlanningGuide
IPv4 exhaustion is complete; the transition to IPv6 is a set of coexistence mechanisms, not a switch to flip. Dual stack where you can, translate where you must, and plan addresses before touching a router.
- Core Router: Role, Architecture and Design RulesGuide
A core router moves packets between aggregation points at line rate and does almost nothing else. Everything about its design, from chassis to redundant control modules, follows from that single job.
- Verifying AI-Written Network Configs Before DeploymentHow-to
A machine-generated configuration reads fluently whether or not it is correct, so treat it like an untrusted patch from a stranger: parse it, diff it, test it, and deploy it with a way back.
- Checking AI-Generated Subnet and ACL Math Before You Use ItHow-to
Ask a chatbot to carve a /22 into VLAN subnets and the answer will look perfect. Often one boundary is off by a block, or a wildcard mask covers twice the range. The fix is not to stop asking, but to check the arithmetic with something that cannot hallucinate.
- Peer Review for AI-Assisted Network ChangesGuide
Change control was built for engineers who make mistakes. AI assistants make different ones, faster and more confidently. The review process does not need to be rebuilt, but it needs to know where to look.
03.1 Orientation
Routing is the part of the network that hosts never see and always depend on. A router forwards packets by destination prefix using a table built from static entries and routing protocols; a redundancy protocol lets two routers share one gateway address so that hosts survive a failure; MPLS wraps packets in labels so a provider can carry many customers' private networks over one core; and IPv6 changes the address plan underneath all of it. The four guides in this section cover those mechanisms in the order an enterprise usually meets them.
VRRP and VSRP explains virtual router election, priority and preemption, the virtual MAC, and Foundry's two extensions: VRRP-E for load-sharing gateways and VSRP, a proprietary Layer 2/3 redundancy protocol that offered sub-second failover as an alternative to spanning tree. MPLS VPN covers labels and LSPs, VRFs, route distinguishers and targets, MP-BGP and the PE/P/CE roles, drawn from the NetIron service-provider material. IPv6 transition is the dual-stack, tunnelling and translation toolkit with an address plan and a deployment checklist, and Core router separates control plane from forwarding plane and explains why a chassis in the core is built the way it is.
Foundry's routers were the NetIron family: the NetIron 400 and 800 Internet core routers around the turn of the century, the IMR 640 for MPLS services, and the XMR and MLX platforms that outlived the company under Brocade and later Extreme Networks. The NetIron profile in the archive covers that hardware; the guides here cover what the hardware did. Routing-capable BigIron and FastIron images also appear where a Layer 3 switch is the practical gateway.
The old site's search engine logged one query more than any other, and enough people linked to the results page for it to survive in the backlink record: ipv6. That URL now resolves to the IPv6 transition guide, which is the honest modern answer to the question those engineers were asking in the mid-2000s. The other recovered documents are the VRRP chapter of the enterprise configuration guide, the VSRP whitepaper, the BGP/MPLS VPN chapter of the IMR 640 service provider guide, the MPLS static LSP command reference and the data centre core solution page.
Each guide ends with verification commands and a short list of the mistakes that cause outages: preemption on a router with slow boot, a missing route target, an untested IPv6 firewall policy, a core with a single management module. The section is deliberately shorter than switching; the wave-two backlog adds OSPF and BGP basics once the first pages have indexed. The site-wide index on the homepage lists what is live today.
How this connects to the provenance section. Routing is where a network first asks whether what it is told is authentic: an announced prefix, a resolved name, a configuration someone or something wrote. DNSSEC, the signature chain a resolver checks before it trusts an answer is the name-layer counterpart of RPKI, and an audit trail that records who changed a router configuration, from where and with what approval is the authorship record every change, AI-assisted or not, should leave behind.