Category: Ip Routing

I’m constantly ranting against large layer-2 domains; recently going as far as saying “we don’t really need all that stuff.” Unfortunately, the IP+Ethernet mentality is so deeply ingrained in every networking engineer’s mind that we rarely ever stop to question its validity.

Let’s fix that and start with the fundamental question: What is Layer-2?

One of the networking engineers using my ExpertExpress to validate their network design had an interesting problem: he was building a multi-tenant VLAN-based private cloud architecture with each tenant having multiple subnets, and wanted to route within the tenant network as close to the VMs as possible (in the ToR switch).

He was using Nexus 5600 as the ToR switch, and although there’s conflicting information on the number of VRFs supported by that switch (verified topology: 25 VRFs, verified maximum: 1000 VRFs, configuration guide: 64 VRFs), he thought 25 VRFs (tenant routing domains) might be enough.

One of my readers is struggling with the aftermath of marketing gimmicks:

We will implement a new network soon, and we're discussing P-routers versus regular routers versus switches. I'm looking for arguments to go one way or the other.

TL&DR: there’s no difference between router and L3 switch.

While the industry press deliberates the disaggregation of Arista and Cisco, and Juniper’s new CEO, Juniper launched a virtual version of its vMX router, which is supposed to have up to 160 Gbps of throughput (as compared to 10 Gbps offered by Vyatta 5600 and Cisco CSR). Can Juniper really deliver on that promise?

One of my readers sent me an interesting challenge:

We have two MPLS providers sending us default routes and it seems like whenever we have problem with SP1 our failover is not happening properly and actually we have to go in manually and influence our traffic to forward via another path.

Welcome to the wondrous world of byzantine routing failures ;)

The discussion in the comments to my LAG versus ECMP post took a totally unexpected turn when someone mentioned BFD failure detection over port channels (link aggregation groups – LAGs).

What’s the big deal?

Bryan sent me an interesting question:

When you have the opportunity to use LAG or ECMP, what are some things you should consider?

He already gathered some ideas (thank you!), and I expanded his list and added a few comments.

Purpose: resiliency or more bandwidth? For resiliency you want fast failure detection and the ability to connect to multiple uplink devices, for more bandwidth, you want better hashing.

My good friend Tiziano complained about the fact that BGP considers next hop reachable if there’s an entry in the IP routing table even though the router cannot even ping the next hop.

That behavior is one of the fundamental aspects of IP networks: networks built with IP routing protocols rely on fate sharing between control and data planes instead of path liveliness checks.

My Trident 2 Chipset and Nexus 9500 blog post must have hit a raw nerve or two – Bruce Davie dedicated a whole paragraph in his Physical Networks in Virtualized Networking World blog post to tell everyone how the whole thing is a non-issue and how everything’s good in the NSX land.

It’s always fun digging into more details to figure out what’s really going on behind the scenes; let’s do it.

I was asked to do a presentation at the recent Slovenian NOG (SINOG) meeting. I did an SDN one at the previous meeting, making NFV the next obvious choice… but I decided to put an interesting spin on it and focused on virtual routers.