Cisco protocol tie breaking gone mad

EdTheLad

This is one of my pet peeves with Cisco, why couldn't they make everything use the highest ip address as the tie breaker.
These are all i could think of right now, please add to the list

Root-bridge, lowest BID
root port election, lowest sender port wins
BGP bestpath, prefer from neighbor with lowest RID
IGMP Querier prefer lowest ip
BGP/OSPF RID highest loopback ip or highest regular ip
BGP TCP session est , highest ip is client
PIM DR highest ip address
HSRP Active router highest ip

Zartanasaurus

Don't forget LACP.

reaper81

Cisco can't control everything though. It's up to the authors of the standards. STP, BGP, PIM are open standards. HSRP is Cisco's baby though.

carterw65

Good point reaper. This topic has always been one of my pet peeves too.

Danielh22185

reaper81 wrote: »

Cisco can't control everything though. It's up to the authors of the standards. STP, BGP, PIM are open standards. HSRP is Cisco's baby though.

Indeed, many of those protocols are not Cisco Proprietary.

NetworkVeteran

EdTheLad wrote: »

This is one of my pet peeves with Cisco, why couldn't they make everything use the highest ip address as the tie breaker.

BGP/OSPF RID highest loopback ip or highest regular ip
BGP TCP session est , highest ip is client
PIM DR highest ip address
HSRP Active router highest ip

L3 protocols do tend to choose the highest IP address.

Root-bridge, lowest BID
root port election, lowest sender port wins

Bridges are L2 and don't necessarily have IPv4 addresses.

PIM DR highest ip address
IGMP Querier prefer lowest ip

In IGMPv1 both DR and Querier roles go to the same router, the one with the highest IP address. In IGMPv2/v3, they divide out the roles, because it's best to leverage the resources of multiple routers if you have them.

If you know the reasons behind the exceptions they're easier to recall.

powmia

This is why we use priorities to make these deterministic without having to remember all of them (of course, this is a certification forum and those elections are always on exams).

Don't forget.... IS-IS -> DIS = highest MAC if no priority is configured.