# IP routing Published articles for IP routing. This is one page of public article previews, not the complete archive. Follow Next page to continue. Summaries are not the original full articles. ## Lab: Implementing VRF-Lite with VXLAN DevFeed: [Lab: Implementing VRF-Lite with VXLAN]() Original publisher: [Read original article]() Published: 2026-06-05T07:21:00Z Content type: tutorial Language: en Sources: [ipSpace.net blog]() Topics: [VXLAN](), [networking](), [IP routing](), [GitHub]() Tags: [apple](), [container](), [evpn](), [free](), [github](), [installation](), [ip-routing](), [netlab](), [protocol](), [routing](), [vxlan]() ### AI overview This lab exercise demonstrates how to implement a VRF-Lite design with VXLAN. The design uses VRF routing protocols over VXLAN-backed VLAN segments and requires IP routing on core switches instead of configuring VLANs and routing protocols for every VRF on every link and device. The lab can run on netlab-enabled infrastructure, a free GitHub Codespace, or an Apple-silicon Mac. ### Source excerpt Did you know that you can implement a VRF-Lite design with VXLAN? All you need are devices that can run VRF routing protocols over VXLAN-backed VLAN segments. Compared to the "traditional" VRF-Lite design, in which you need a set of VLANs on every link and every device running the routing protocol for every VRF, the VXLAN-based design needs just IP routing on the core switches, resulting in a design that's pretty close to what we were building with DMVPN (without IPsec and NHRP complications). Read more ... ## ARP Issues in EVPN Centralized Routing Design DevFeed: [ARP Issues in EVPN Centralized Routing Design]() Original publisher: [Read original article]() Published: 2026-05-05T05:45:00Z Content type: article Language: en Sources: [ipSpace.net blog]() Topics: [evpn](), [networking](), [IP routing](), [Routing (disambiguation)]() Tags: [arp](), [ethernet](), [evpn](), [ip-routing](), [routing]() ### AI overview This article examines ARP and traffic-flooding problems in a centralized routing design using EVPN MAC-VRFs. It explains the expected packet flow through a spine switch and describes how implementations that do not advertise VLAN IP/MAC addresses can prevent switches from locating the gateway MAC, causing inter-subnet traffic to be flooded. ### Source excerpt Adding IRB to a EVPN MAC-VRFs (the fancy way of saying stretched VLANs) seems like a no-brainer: Add IP addresses to VLAN interfaces Optionally add a shared anycast gateway Declare "Mission Accomplished" (and try to ignore the inevitable phone call at 2 AM on a Sunday night) Making that work in a multi-vendor environment is even more fun1, as I sadly discovered when creating the EVPN lab exercises or trying to figure out why some EVPN implementations were failing netlab EVPN integration tests. Read more ... ## netlab 26.04: EXOS, BGP Prefix Origination, More Static Routes DevFeed: [netlab 26.04: EXOS, BGP Prefix Origination, More Static Routes]() Original publisher: [Read original article]() Published: 2026-04-13T05:28:00Z Content type: release Language: en Sources: [ipSpace.net blog]() Topics: [Release notes](), [BGP](), [IP routing](), [Routing (disambiguation)](), [networking](), [Vagrant](), [evpn](), [VXLAN](), [Containerlab topology]() Tags: [bgp](), [evpn](), [ip-routing](), [linux](), [netlab](), [release](), [release-notes](), [routing](), [vagrant](), [vxlan]() ### AI overview The netlab 26.04 release adds support for Extreme Networks EXOS, new BGP advertisement and origination capabilities, additional platforms with static-route support, and EVPN/VXLAN over IPv6 support in FRRouting. It also expands routing configuration support for several platforms. ### Source excerpt netlab release 26.04 is out. Here are the highlights: Extreme Networks EXOS is supported as a Vagrant box or containerlab node with OSPF, VLAN, and VRRP configuration (by Seb d'Argoeuves). The new bgp.advertise node attribute allows you to advertise networks in the IP routing table into BGP. It's supported on most platforms. The bgp.originate attribute is now dual-stack and VRF-aware, allowing you to originate IPv4 and IPv6 prefixes into per-VRF BGP instances. New platforms with static route support: FortiOS (by Aleksey Popov), Nexus OS, Nokia SR OS, Nokia SR Linux. OpenBSD got discard static routes. Read more ... ## IPv4 ECMP Works on Arista cEOS Release 4.35.2F DevFeed: [IPv4 ECMP Works on Arista cEOS Release 4.35.2F]() Original publisher: [Read original article]() Published: 2026-03-12T09:09:00Z Content type: opinion Language: en Sources: [ipSpace.net blog]() Topics: [IP routing](), [networking](), [Linux]() Tags: [ip](), [ip-routing](), [ipv4](), [linux-kernel](), [mpls](), [release](), [switching]() ### AI overview The article reports that IPv4 ECMP works on Arista cEOS release 4.35.02F, with traffic spreading across multiple nodes in the author's lab topology. It also observes that forwarded traffic uses ECMP while locally originated traffic does not, despite different routing-table entries. ### Source excerpt When I wrote about the anycast-ECMP-in-MPLS behavior in 2011, I had to use Cisco IOS to prove that ECMP worked, since Arista cEOS (running the Linux kernel for IP forwarding) didn't install more than one equal-cost path into the Linux forwarding table. Arista cEOS got better in the meantime; IPv4 ECMP works like a charm on cEOS release 4.35.02F. With the same lab topology I'd used in 2021, I was able to see the traffic spread across multiple nodes: Read more ... ## On MPLS Paths, Tunnels and Interfaces DevFeed: [On MPLS Paths, Tunnels and Interfaces]() Original publisher: [Read original article]() Published: 2026-01-20T06:29:00Z Content type: opinion Language: en Sources: [ipSpace.net blog]() Topics: [Network](), [MPLS-TE](), [Routing (disambiguation)](), [IP routing](), [Protocol (disambiguation)](), [VXLAN]() Tags: [gre](), [ip-routing](), [mpls](), [network](), [networking-fundamentals](), [protocol](), [routing](), [vxlan]() ### AI overview The article explains the fundamental difference between overlay tunnels such as GRE, IPsec, and VXLAN and MPLS paths. Tunnels connect separate overlay segments across an underlay, while MPLS paths improve forwarding within the same network; routing protocols are used differently in these designs. ### Source excerpt One of my readers attempted to implement a multi-vendor multicast VPN over MPLS but failed. As a good network engineer, he tried various duct tapes but found that the only working one was a GRE tunnel within a VRF, resulting in considerable frustration. In his own words: How is a GRE tunnel different compared to an MPLS LSP? I feel like conceptually, they kind of do the same thing. They just tunnel traffic by wrapping it with another header (one being IP/GRE, the other being MPLS). Instead of going down the "how many angels are dancing on this pin" rabbit hole (also known as "Is MPLS tunneling?"), let's focus on the fundamental differences between GRE/IPsec/VXLAN tunnels and MPLS paths. Read more ... ## Arista EOS Hates a Routing Instance with No Interfaces DevFeed: [Arista EOS Hates a Routing Instance with No Interfaces]() Original publisher: [Read original article]() Published: 2025-09-18T05:20:00Z Content type: article Language: en Sources: [ipSpace.net blog]() Topics: [BGP](), [bug](), [debug](), [Ansible](), [IP routing](), [Containers](), [virtual machines]() Tags: [ansible](), [bgp](), [bug](), [containers](), [debug](), [ip-routing](), [netlab](), [virtual-machines]() ### AI overview A debugging investigation finds that Arista EOS fails to configure BGP and enable IP routing when the default VRF has no interfaces. The issue occurs in container and virtual-machine deployments across multiple EOS releases, while the error message is misleading. ### Source excerpt I always ask engineers reporting a netlab bug to provide a minimal lab topology that would reproduce the error, sometimes resulting in "interesting" side effects. For example, I was trying to debug a BGP-related Arista EOS issue using a netlab topology similar to this one: defaults.device: eos module: [ bgp ] nodes: a: { bgp.as: 65000 } b: { bgp.as: 65001 } Imagine my astonishment when the two switches failed to configure BGP. Here's the error message I got when running the netlab's deploy device configurations Ansible playbook: Read more ... ## How Cisco IOS/XE and Arista EOS Handle Multiple IP Addresses in "ip host" Configuration DevFeed: [How Cisco IOS/XE and Arista EOS Handle Multiple IP Addresses in "ip host" Configuration]() Original publisher: [Read original article]() Published: 2025-09-11T07:51:00Z Content type: article Language: en Sources: [ipSpace.net blog]() Topics: [networking](), [Cisco](), [IP routing]() Tags: [cisco](), [ethernet](), [ip](), [ip-routing](), [mapping](), [netlab](), [networking](), [ospf](), [router]() ### AI overview The article examines how Cisco IOS Classic, Cisco IOS/XE, and Arista EOS handle multiple IP addresses in the ip host configuration command. It reports differing behavior in host displays, ping target selection, and address ordering, based on a two-router OSPF lab. ### Source excerpt Since time immemorial, I have used the ip host router configuration command to get host-to-IP mappings in networking labs without going through the hassle of setting up a DNS server. Some devices even accepted multiple IP addresses in the ip host command, allowing you to list all router interfaces in a single command and get reverse (IP-to-host) mapping working like a charm. Or so I thought 🤦♂ It turns out I'm too old, and what I know is sometimes no longer true. It seems that the last implementation working as I expected is Cisco IOS Classic ☹ Read more ... ## Response: True Unnumbered Interfaces DevFeed: [Response: True Unnumbered Interfaces]() Original publisher: [Read original article]() Published: 2025-05-22T05:55:00Z Content type: article Language: en Sources: [ipSpace.net blog]() Topics: [IS-IS](), [networking](), [Linux](), [Routing (disambiguation)]() Tags: [configuration](), [interface](), [ip-routing](), [ipv4](), [ipv6](), [is-is](), [linux](), [networking-fundamentals](), [ospf](), [protocol](), [router](), [routing]() ### AI overview This article explains why routers commonly associate IP addresses with interfaces and examines how IS-IS handles unnumbered interfaces. It contrasts IS-IS with OSPF and describes IPv4 next-hop requirements, IPv6 link-local operation, and implementation-specific approaches such as those used by EBGP. ### Source excerpt Hendrik left an interesting comment on my Running IS-IS over Unnumbered Ethernet Interfaces blog post: FRRouting (Linux) with pure IS-IS, the only way it currently (10.3) works is to copy the loopback IPv4 address to the interfaces that you need to do IPv4 routing on. The OpenFabric (IS-IS "extension" draft) does support true unnumbered interfaces and routes IPv6. Let's unpack this. There are (at least) four reasons a router needs an address associated with an interface1: Read more ... ## OSPF Summary LSA Loop Prevention DevFeed: [OSPF Summary LSA Loop Prevention]() Original publisher: [Read original article]() Published: 2025-04-30T06:17:00Z Content type: tutorial Language: en Sources: [ipSpace.net blog]() Topics: [networking](), [Protocol (disambiguation)](), [IP routing](), [Routing (disambiguation)]() Tags: [ip-routing](), [networking](), [ospf](), [protocol](), [routing]() ### AI overview This article explains how OSPF prevents an ABR from advertising a Type-3 summary LSA generated from area 1 prefixes back into area 1. The route-selection process prefers intra-area paths over inter-area paths, so the ABR does not use the inter-area route for summary-LSA generation. ### Source excerpt A networking-focused entity known only as humblegrumble sent me the following question after reading my When OSPF Becomes a Distance Vector Protocol article: How do A1 and A2 know not to advertise a Type-3 summary LSA generated from area 1 prefixes back into area 1? He's right. There is no "originating area" information in the type-3 LSA, so how does an ABR know not to reinsert the type-3 LSA generated by another ABR back into the area? TL&DR: The OSPF route selection process takes care of that. Read more ... ## Comparing IP and CLNP: Network State Summarization DevFeed: [Comparing IP and CLNP: Network State Summarization]() Original publisher: [Read original article]() Published: 2025-03-19T06:59:00Z Content type: article Language: en Sources: [ipSpace.net blog]() Topics: [IP routing](), [networking](), [IS-IS](), [Protocol (disambiguation)](), [BGP]() Tags: [bgp](), [ip-routing](), [ipv6](), [is-is](), [networking-fundamentals](), [routing](), [tcp-ip]() ### AI overview This article compares how TCP/IP and CLNP summarize network state in routing protocols. It explains that TCP/IP routing generally provides subnet, intra-area, and inter-area summarization levels, while most CLNP networks used two levels based on node and area addresses, with BGP enabling additional levels in either design. ### Source excerpt In the previous blog posts, we discussed how TCP/IP and CLNP reach adjacent nodes and build ARP/ND/ES caches and how they reach off-subnet nodes. Now, let's move from the network edge into the network core and explore how the two protocol stacks reduce the amount of information they have to propagate in routing protocols. While I'm not exactly an OSI fan, I must admit they got many things right (and IPv6 copied those ideas), but TCP/IP is a clear winner in this aspect. Read more ... ## Cisco VRRPv3 IPv6 Configuration Requirements DevFeed: [Cisco VRRPv3 IPv6 Configuration Requirements]() Original publisher: [Read original article]() Published: 2025-01-27T07:20:00Z Content type: opinion Language: en Sources: [ipSpace.net blog]() Topics: [Cisco](), [configuration](), [Command-line interface]() Tags: [cisco](), [cli](), [configuration](), [ip-routing](), [ipv6](), [netlab]() ### AI overview The article examines Cisco IOS and Nexus OS requirements for configuring VRRPv3 with IPv6. It explains that a link-local address must be configured manually as the primary VRRP address and discusses interoperability considerations for using a MAC-derived link-local address. ### Source excerpt I spent way too much time ironing out the VRRPv3 quirks on the dozen (or so) platforms supported by netlab. This is the second blog post describing some of the ridiculous stuff I had to deal with. This is how you configure the basic VRRPv3 parameters for IPv4 on a Cisco IOS/XE device: VRRPv3 IPv4 configuration on Cisco IOS interface GigabitEthernet0/1 vrrp 217 address-family ipv4 address 172.16.33.42 You would expect something similar for IPv6, right? You'd be right if you were working with Arista EOS: Read more ... ## BGP PIC Edge Requires Per-Prefix or Per-CE VPN Labels DevFeed: [BGP PIC Edge Requires Per-Prefix or Per-CE VPN Labels]() Original publisher: [Read original article]() Published: 2024-12-04T08:09:00Z Content type: article Language: en Sources: [ipSpace.net blog]() Topics: [BGP](), [MPLS VPN](), [Network]() Tags: [bgp](), [blog-post](), [ip-routing](), [mpls](), [mpls-vpn](), [network]() ### AI overview This blog post explains how BGP PIC Edge is intended to switch traffic to a backup PE-CE path before full network convergence. It argues that the mechanism needs per-prefix or per-CE VPN labels; per-VRF labels would create a temporary micro-loop. ### Source excerpt This blog post discusses an old arcane question that has been nagging me from the bottom of my Inbox for almost exactly four years. Please skip it if it sounds like Latin to you, but if you happen to be one of those readers who know what I'm talking about, I'd appreciate your comments. Terminology first: Prefix Independent Convergence allows entries in the forwarding table to point to shared next hops (or next-hop groups), reducing the FIB update bottleneck when changing the next hop for a large number of prefixes (for example, when dealing with a core link failure). More details in the initial blog post and PIC applicability to fast reroute. PIC Edge (as defined by vendor marketing) is the ability to switch to a backup CE route advertised to a backup PE router before the network convergence is complete. Here's (in a nutshell) how PIC Edge is supposed to work: Read more ... ## Running Routing Protocols over Tunnels DevFeed: [Running Routing Protocols over Tunnels]() Original publisher: [Read original article]() Published: 2024-11-05T07:14:00Z Content type: article Language: en Sources: [ipSpace.net blog]() Topics: [networking](), [Routing (disambiguation)](), [Protocol (disambiguation)](), [BGP](), [IS-IS](), [MPLS-TE](), [MPLS VPN](), [evpn](), [VXLAN](), [Reason]() Tags: [bgp](), [evpn](), [ip-routing](), [is-is](), [mpls](), [mpls-te](), [ospf](), [protocol](), [recursion](), [routing](), [vxlan]() ### AI overview This article explains why routing protocols over tunnels can cause recursive routing and infinite encapsulation. It distinguishes traffic-engineering and IPsec tunnels from VPN designs, where routing protocols exchange customer and transport prefixes using separated address spaces or families. ### Source excerpt James got confused by a statement made by Hannes Gredler in his IS-IS book: Things behave really badly if the total IGP cost over the tunnel undermines the total topologies' cost. What happens next is that the tunnel "wraps" around itself, ultimately causing a meltdown of the entire network. Let's unpack that, starting with "Why would you need a tunnel?" Read more ... ## Routing Table and BGP RIB on SR Linux DevFeed: [Routing Table and BGP RIB on SR Linux]() Original publisher: [Read original article]() Published: 2024-09-04T05:24:00Z Content type: article Language: en Sources: [ipSpace.net blog]() Topics: [BGP](), [IP routing](), [networking]() Tags: [bgp](), [ip-routing](), [network](), [routing]() ### AI overview The article examines how SR Linux handles routing information, contrasting its behavior with traditional network operating systems and FRRouting. In an SR Linux lab, system routes also appear in the BGP RIB, while an OSPF route is present in the BGP RIB without being advertised to the adjacent BGP router. ### Source excerpt Ages ago, I described how "traditional" network operating systems used the BGP Routing Information Base (BGP RIB), the system routing table (RIB), and the forwarding table (FIB). Here's the TL&DR: Routes received from BGP neighbors are stored in BGP RIB. Routes redistributed into BGP from other protocols are (re)created in the BGP RIB. BGP selects the best routes in BGP RIB using its convoluted set of rules. Best routes from the BGP RIB are advertised to BGP neighbors Best routes from the BGP RIB compete (based on their administrative distance) against routes from other routing protocols to enter the IP routing table (system RIB) Routes from the system RIB are copied into FIB after their next hops are fully evaluated (a process that might involve multiple recursive lookups). Read more ... ## Response: The Usability of VXLAN DevFeed: [Response: The Usability of VXLAN]() Original publisher: [Read original article]() Published: 2024-08-12T05:50:00Z Content type: opinion Language: en Sources: [ipSpace.net blog]() Topics: [VXLAN](), [networking](), [datacenter](), [Scalability](), [IP routing]() Tags: [data-center](), [fabric](), [ip-routing](), [network](), [networking](), [routing](), [scalability](), [vxlan]() ### AI overview The article argues that VXLAN can be useful even when an enterprise network is not reaching VLAN scalability limits. It identifies VLAN-only data center fabrics' reliance on STP and MLAG as significant drawbacks, and explains that VXLAN fabric transport enables IP routing and ECMP load balancing. It also notes that small VXLAN fabrics do not necessarily need EVPN. ### Source excerpt Wes made an interesting comment to the Migrating a Data Center Fabric to VXLAN blog post: The benefit of VXLAN is mostly scalability, so if your enterprise network is not scaling... just don't. The migration path from VLANs is to just keep using VLANs. The (vendor-driven) networking industry has a huge blind spot about this. Paraphrasing the famous Dinesh Dutt's Autocon1 remark: I couldn't disagree with you more. Read more ... ## Repost: Campus-Wide Wireless Roaming with EVPN DevFeed: [Repost: Campus-Wide Wireless Roaming with EVPN]() Original publisher: [Read original article]() Published: 2024-04-22T06:05:00Z Content type: article Language: en Sources: [ipSpace.net blog]() Topics: [evpn](), [VXLAN](), [Networks](), [Testing](), [DHCP]() Tags: [dhcp](), [evpn](), [ip-routing](), [networks](), [testing](), [vxlan]() ### AI overview This repost presents details from a large-scale campus wireless roaming test using EVPN and VXLAN tunnels to a central aggregation point. The reported recommendations include dedicated aggregation switches, tunneled client traffic, and wireless DHCP broadcast-to-unicast conversion. ### Source excerpt As a response to my LISP vs EVPN: Mobility in Campus Networks blog post, Route Abel provided interesting real-life details of a large-scale campus wireless testing using EVPN and VXLAN tunnels to a central aggregation point (slightly edited): I was arguing for VxLAN EVPN with some of my peers, but I had no direct hands-on knowledge of how it would actually perform and very limited ability to lab it on hardware. My client was considering deploying Campus VxLAN, and they have one of the largest campuses in North America. Read more ... ## FRRouting Claims IBGP Loopbacks Are Inaccessible DevFeed: [FRRouting Claims IBGP Loopbacks Are Inaccessible]() Original publisher: [Read original article]() Published: 2024-03-27T07:10:00Z Content type: article Language: en Sources: [ipSpace.net blog]() Topics: [networking](), [IP routing](), [BGP](), [Networks](), [Routing (disambiguation)](), [systems]() Tags: [bgp](), [blog-post](), [ip-routing](), [networking](), [networks](), [ospf](), [routing](), [systems]() ### AI overview The article examines how FRRouting handles prefixes advertised through both OSPF and IBGP. In the described case, FRRouting places both routes in the IP routing table but rejects the IBGP route for a loopback prefix because it considers the BGP next hop inaccessible, possibly due to recursive routing prevention logic. ### Source excerpt Last week, I explained the differences between FRRouting and more traditional networking operating systems in scenarios where OSPF and IBGP advertise the same prefix: Traditional networking operating systems enter only the OSPF route into the IP routing table. FRRouting enters OSPF and IBGP routes into the IP routing table. On all platforms I've tested, only the OSPF route gets into the forwarding table1. One could conclude that it's perfectly safe to advertise the same prefixes in OSPF and IBGP. The OSPF routes will be used within the autonomous system, and the IBGP routes will be propagated over EBGP to adjacent networks. Well, one would be surprised 🤦♂ Read more ... ## FRRouting RIB and FIB DevFeed: [FRRouting RIB and FIB]() Original publisher: [Read original article]() Published: 2024-03-20T06:39:00Z Content type: tutorial Language: en Sources: [ipSpace.net blog]() Topics: [Network](), [networking](), [IP routing](), [Routing (disambiguation)](), [BGP](), [Kernel](), [Linux]() Tags: [bgp](), [ip-routing](), [kernel](), [linux](), [network](), [networking](), [ospf](), [routing]() ### AI overview This article explains how FRRouting handles routes from protocols such as BGP and OSPF across its IP routing table, the Linux kernel routing table, and the forwarding table. It also shows how local interface routes can be viewed with ip route list table local. ### Source excerpt This is how we described the interactions between routing protocol tables, RIB, and FIB in the ancient times: Routing protocols compute the best paths to all known prefixes. These paths compete for entry in the routing table. The path(s) with the lowest administrative distance win. The entries from the routing table are fully evaluated (in particular, their next hops) and entered in the forwarding table. Let's use a simple BGP+OSPF network to illustrate what I'm talking about: Read more ... ## Interface EBGP Sessions on Arista EOS DevFeed: [Interface EBGP Sessions on Arista EOS]() Original publisher: [Read original article]() Published: 2024-03-19T06:48:00Z Content type: tutorial Language: en Sources: [ipSpace.net blog]() Topics: [BGP](), [IP routing](), [networking]() Tags: [bgp](), [examples](), [guide](), [ip-routing](), [routing]() ### AI overview A configuration guide for interface EBGP sessions on Arista EOS. It explains that the sessions use TCP over IPv6 link-local addresses while carrying IPv4 routes, and outlines the Arista cEOS 4.31.2F configuration requirements. ### Source excerpt Arista EOS and Cisco Nexus OS got interface EBGP sessions years after Cumulus Linux. While they're trivially easy to configure on FRRouting (the routing daemon used by Cumulus Linux), getting them to work on Arista EOS is a bit tricky. To make matters worse, my Google-Fu failed me when I tried to find a decent step-by-step configuration guide; all I got was a 12-minute video full of YouTube ads. Let's fix that. Read more ...