[c-nsp] Fast IGP on 6500 & gigE

[Marcus.Gerdon]

Hi,

you've written most routers are dual-attached, so the concern mostly is failure detection and not re-establishment of a neighbor I think. If you go into debounce or carrier-delay you'll raise the convergence time as a link failure will be ignored for a short time before processes are notified.

OSPF should immediately react on an link-down event, so I'd try to speed it up this way. If you use 2 separate SVI for the 2 connections and each VLAN has only 1 port it is allowed in (either a single access port or exactly 1 trunk port) the SVI should go down along with that single port.

Playing around the timers I keep for last resort - as there's always the risk to de-stabilize the network seriously (I've seen people trying to get the last second out of a protocol resulting in occasional burn-downs far too often).


regards,

Marcus
 

> -----Ursprüngliche Nachricht-----
> Von: cisco-nsp-bounces at puck.nether.net 
> [mailto:cisco-nsp-bounces at puck.nether.net] Im Auftrag von Phil Mayers
> Gesendet: Montag, 16. März 2009 17:45
> An: cisco-nsp at puck.nether.net
> Betreff: [c-nsp] Fast IGP on 6500 & gigE
> 
> All,
> 
> Given a mix of 6748-SFP, 6704 and 6716 linecards, with SXI 
> software, and 
> OSPF over SVIs, what are people successfully using to speed 
> up link loss 
> and subsequent IGP convergence?
> 
> Our config broadly looks like:
> 
> int Vlan38xx
>    description p2p to another router
>    ip address 192.168.0.2 255.255.255.254
>    ip ospf network point-to-point
> 
> int Te1/1
>    switchport
>    switchport mode trunk
>    switchport trunk native vlan 38xx
> 
> router ospf 1
>    ispf
>    nsf
>    network 192.168.0.0 0.0.0.255
> 
> ....and then the various LDP & BGP configs on top. I'm 
> assuming I want 
> some combination of:
> 
>   1. debounce / carrier-delay (what's the difference) on the gigE
>   2. IP event dampening on the SVI
>   3. faster timers on the SFP process; possibly as a 
> conservative start:
> 
> timers throttle spf 10 100 5000
> timers throttle lsa all 10 100 5000
> timers lsa arrival 80
> 
> The idea is that most routers are dual-attached, so I just want to 
> underlying IGP to converge quickly. I'll tackle the LDP and 
> BGP later...
> 
> I'm not able to use BFD (since it doesn't work on SVIs under SXI) and 
> I'm only worried about physical link-down - we don't have any weird 
> layer2 between routers except in a few out-of-the way places, 
> and they 
> can just suffer.
> 
> I realise some of these answers are "it depends" on the size of your 
> network; there are ~25 routers participating in the OSPF, all 
> reasonably 
> recent and modern, it's a single area 0 design, and it has ~58 p2p & 
> loopbacks (via router LSAs) another 18 E2 routes.
> 
> It seems to take ~6msec for an OSPF adjacency to form between two 
> routers, almost all of which is in INIT->2WAY so I'm guessing SPF is 
> going to be pretty quick.
> 
> Suggestions welcome, although "ask Cisco to tell you" is less 
> helpful; 
> I'd like to have some independent understanding of how we 
> arrived at the 
> numbers, and be able to repeat the process in future ;o)
> _______________________________________________
> cisco-nsp mailing list  cisco-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-nsp
> archive at http://puck.nether.net/pipermail/cisco-nsp/
>