For iBGP number of peers (i.e. the number of BGP routers inside an AS), the only significant limiting factor is that iBGP peers must be fully meshed (N.B.: not directly interconnected! An iBGP peering can span all the hops you can fit into the IP TTL field) – because it is the only way for iBGP to prevent… Read More »
In this post I’ll try to make an educated guess about what happens with Hulc LED process and why it appears to consume 20-30% CPU on Cisco 2960(S/X/XR/RX) switches. (N.B.: the issue appears to be present on Cisco 3750 / 3560 platforms as well) Symptoms If you monitor your switch via SNMP, you may quickly notice constantly elevated… Read More »
Recently, I tested a Cisco 6500 switch in a fan-less configuration, to see how long it can go. DISCLAIMER: DO NOT TRY TO DO IT. This is a stupid idea and it will void warranty / would be a perfectly valid reason for Cisco to decline RMA (in my opinion at least). Running a switch without fans will… Read More »
There is an interesting problem with Cisco 6500 VSS clusters: generally, switchover between nodes is fast enough and only a few packets are lost. NSF&SSO algorithms help a lot to achieve that. But if you configure a feature that doesn’t support SSO for some reason, the flap becomes more noticeable. In this post I’m trying to make an… Read More »
Recently I attended a two-day class on Cisco HyperFlex by Tomaz Klancnik from NIL. It was quite interesting and packed with information about this new Cisco’s system. Here are the notes I took during the lectures and the labs. General Notes about Cisco HyperFlex Not developed internally; Not a complete acquisition / spin-in; software developed by Springpath https://springpathinc.com/resources.php… Read More »
An EtherChannel is a way to use multiple physical interfaces as a single logical one. That logical one appears as a single interface to MAC table, STP and management plane. That solves two main concerns: it adds bandwidth and it prevents STP from considering several parallel links a loop, thus preventing it from being blocked.
Apparently, there are several very distinct topics in routing which have the word “demand” in them. First, there is Cisco On-Demand Routing quasi-protocol, and then there are on-demand circuits which routing protocols must treat differently. Last but not least, the on-demand circuits are used for Routing Backup.
Sometimes while you do routing, you want to do it in a destination-based way and also differentiate routing for different sub-autonomous systems in your AS. Well, such behavior can be enforced by PBR, but it is not that scalable and it lacks some of the nicer things dynamic routing protocols bring to the table. Enter Virtual Routing and… Read More »