Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!magnus.acs.ohio-state.edu!csn!boulder!daemon From: P.Elford@aarnet.edu.au (Peter Elford) Newsgroups: comp.dcom.sys.cisco Subject: Routing query Message-ID: <34372@boulder.Colorado.EDU> Date: 20 Apr 91 06:19:01 GMT Sender: news@boulder.Colorado.EDU Lines: 120 The Australian Academic and Research Network (AARNet) is currently configured as a star of stars, ie. QLD | | NSW ACT | / \ | / \|/ WA -----------N---TAS /| P----> 128K satellite to USA / | | / -+---+---+- SA | VIC Each of the acronyms represents an AGS router that has links to all the AARNet members within a particular state. The "N" is also an AGS (the national hub) and "P" is a Proteon that terminates our link to FIX-WEST. All but one of the routers is runing 8.1(19) (VIC is an AGS+ with 8.2(1)). All the links are 48K except for a short ethernet between N, VIC and P, and the link to the US. Routing in this enviroment is VERY simple. We use RIP to pass network routes up from the individual member sites to the state hubs, and from them to the national hub. The national hub, VIC and the proteon are the only routers that have a route for all Australian network numbers; all the other state hubs only have routes to the networks within their state. The router at each member site has a static route to default that points at the state hub and the state hubs have a static route to default that points at the national hub. The Proteon sends out a route to 132.160 (the PACCOM network that links us to the US) and the national hub uses this as its default network. We are about to install two E1 circuits as shown below: ACT NATIONAL +---------------+ 2Mb +---------------+ NSW | 139.130.188.2 +---------+ 139.130.188.1 | +---------------+ 2Mb | | | | | 139.130.192.2 +---------+ 139.130.192.1 | | | | | 48K +---------------+ | | | 139.130.72.2 +-----------------------------------+ 139.130.72.1 | +---------------+ +---------------+ The 48K between ACT and the national hub will be retired when the 2Mb lines go in, but the 48K between NSW and the national hub will be retained for backup. HOW DO WE SET UP OUR ROUTING TO DO DYNAMIC FAILOVER TO THE 48K IF ONE OF THE 2Mb LINKS DIES ? My current thinking goes as follows: A) Stick with RIP. We can only do this if there is some method of artificially increasing the hop count of routes sent from NSW to the national hub over the 48K line. The "offset-list" parameter only allows you to fiddle routing metrics on a per network, rather than per interface, basis. IS THIS TRUE ? CAN WHAT I WANT BE DONE ? B) Fire up IGRP to be able to dynamically detect the failure of one of the 2Mb lines. NSW and ACT routes will have to distributed between all three routers but since most of them have are learnt via RIP, to redistribute them using IGRP we will have to use a "default-metric" for them all. DOES THIS MEAN THAT ALL RIP ROUTES REDISTRIBUTED BY IGRP WILL HAVE THE SAME METRIC REGARDLESS OF WHICH INTERFACE THEY GO OUT OVER ? (which, of course, negates the reason why we were going to run RIP in the first place :-). I guess the another option would be to run IGRP throughout AARNet, but that's a pretty big change just for a new link! Also, we will have to be a little smarter about how "default" is handled. Obviously the static default routes will have to be removed in the ACT and NSW routers. Since ALL routers in the network ignore any RIP default routes sent to them (over any interface, remember we are running 8.1 ...) we can probably safely use IGRP to pass around a dynamic default route. It would be nice to use the PACCOM network as our "default-network" but that would mean that if the satellite link went down then ACT and NSW would not have a route back to the national hub. We could of course pass routes for all Australian network numbers to ACT and NSW from the national hub, but we have just put in place a whole bunch of filters to avoid this (and the issue of metrics when redistributing RIP to IGRP appears again, but this is less of a problem in this case since the other states are all still in a star topology). ARE THERE ANY OTHER WAYS OF PASSING DEFAULT GATEWAY INFORMATION AROUND ? Would this work ? router igrp 1221 redistribute static default-network 132.160.0.0 ! ip route 132.160.0.0 139.130.x.y ie. advertise 132.160 via IGRP, marked as an "exterior route" but don't rely on it being passed dynamically to us from the Proteon. Finally, on a related issue: DOES AN IGRP "EXTERIOR ROUTE" OVERRIDE A RIP DEFAULT NETWORK (0.0.0.0) ? (I assume so because IGRP routes have a smaller administrative distance than RIP derived ones by default). Comments gratefully appreciated, Peter Elford, e-mail: P.Elford@aarnet.edu.au Network Co-ordinator, phone: +61 6 249 3542 Australian Academic Research Network, fax: +61 6 247 3425 c/o, Computer Services Centre, pager: +61 6 245 3035 Australian National University post: PO Box 4 Canberra, AUSTRALIA Canberra 2601