Re: Question on OSPF virtual-links computed via a router with in RFC-3137 "overload"
Erblichs <erblichs@EARTHLINK.NET> Fri, 30 July 2004 23:06 UTC
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Date: Fri, 30 Jul 2004 16:07:49 -0700
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From: Erblichs <erblichs@EARTHLINK.NET>
Subject: Re: Question on OSPF virtual-links computed via a router with in RFC-3137 "overload"
To: OSPF@PEACH.EASE.LSOFT.COM
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Group, Sorry... > the delay should each time the delay should increase each time ... Mitchell Erblich --------------- Erblichs wrote: > > Group, > > My two cents.. > > The level of "overload" is adjustable by > adjusting the cost of the advertised route. > This way some routers may use the route as > as preferred even when another is available. > > If a router is OVERLOADED, it is concieveable > that the former may be the alternative. If it > is, then link could be advertised with MAXAGE > for the duration of the overload, and be > re-advertised after some period of time that > the overload state is no longer present. The > delay should minimize the route flapping, and > the delay should each time the route is pre-aged > or its cost adjusted due to overload. > > Please realize that each time that the route is > re-advertised, minimally their is overhead resources > that will be consumed by the other routers, and thus > routers should protect themselves from routes that are > repeatedly being re-advertised. > > Mitchell Erblich > ------------------- > > Liem Nguyen wrote: > > > > Don, > > > > On Fri, Jul 30, 2004 at 04:53:28PM -0400, Don Goodspeed wrote: > > > All, > > > > > > I have a question on a topology where I mix virtual-links with > > > a router set in a RFC-3137 compliant "stub router" or "overload" > > > state. > > > > > > BB<->Router A <--> Router B <--> Router C <--> Router D > > > Area 0 ABR Area 1 Area 1 ABR Area 2 > > > > > > If everything lines up, Router A is an ABR between area 0 > > > and area 1. Router C is an ABR between area 1 and area 2. > > > > > > I configure a virtual-link between routers A and C so router > > > D can communicate to the backbone routers in area 0. > > > > > > If Router B is then set to an overload state compliant with > > > RFC-3137, it advertises it's transit links with a metric of > > > 65535. Router C then computes the cost of the virtual-link > > > to A as 65535 + the metric of its link to B. > > > > > > My question is should the virtual-adjacency between A and C > > > be declared down, or should A and C advertise the virtual-link > > > metric in their router LSAs as 65535? This issue does not > > > > The latter. > > Note that RFC3137 is a little different than the IS-IS overload > > feature in that RFC3137 only discourages transit traffic through the > > "stub" router; however, if there are no alternate paths, > > the "stub" router can still be used. > > > > Liem > > > > > seem to be covered in either RFC-3137 or RFC-2328. > > > > > > This could also be done without an RFC-3137 situation by > > > setting the path metrics such that the cost of the virtual- > > > link also exceeds 65535. > > > > > > My feeling is that since the path metric exceeds 65535 the > > > virtual adjacency should be torn down (since there is no better > > > path between A and C). > > > > > > Any other opinions? > > > Don > > > > > > _______________________________________________ > > > Join Excite! - http://www.excite.com > > > The most personalized portal on the Web! > > > > -- > > > > Liem Nguyen