[c-nsp] OSPF clarification

[Eric Gauthier]

Alex,

If this is a big concern and you have the option, 
check out IS-IS.

Eric :)


On Mon, Nov 30, 2009 at 03:09:31PM -0000, Alex wrote:
> Drew,
> If your VLANs are all covered by "network X.Y.Z.W area V" command under 
> "router ospf T" then they all are represented as Type-1/Type-2 LSA in OSPF 
> LSDB.
> And every time a VLAN goes down, LSA-1/2 are reflooded with Age=MaxAge 
> (default 3600 sec).
> When this VLAn goes back up, LSA-1/2 are recreated and reflooded again.
> Every time this happens, all OSPF routers in given area must recalculate 
> their SPF, then put OSPF routes in a routing table with new timestamp.
> I'd suggest to use OSPF "network" statement for core VLANs only, edge VLANs 
> should be injected with "redistrubute connected/static" statement (this 
> creates Type-5 LSA for edge VLANs which does not affect SPF).
> HTH
> Rgds
> Alex
> 
> 
> --------------------------------------------------
> From: "Drew Weaver" <drew.weaver at thenap.com>
> Date: 30 November 2009 14:39
> To: "Cisco-nsp" <cisco-nsp at puck.nether.net>
> Subject: [c-nsp] OSPF clarification
> 
> >Hi,
> >
> >If you have your entire network in a single area (area 0), is it normal 
> >that when a VLAN on any switch in that area flaps that all of your routes 
> >in OSPF 'reset'?
> >
> >I don't mean a 'neighbor' VLAN, I mean just any old VLAN with an IP 
> >address assigned to it.
> >
> >Last update from x.x.x.x on Vlan4061, 00:08:42 ago
> >
> >I mean the 'timers' seem to reset for every single route in OSPF anytime a 
> >single VLAN anywhere goes down.
> >
> >If this is intended, which I am still not sure of, what would be the 
> >proper way to 'area' a datacenter?
> >
> >It doesn't seem like there would be a way to do it so that just the route 
> >attached to said VLAN that is flapping would be removed/re-inserted unless 
> >you put each VLAN in a separate area.
> >
> >thanks,
> >-Drew
> >
> >
> >
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