From: Brian Hanson (bhanson@xxxxxxxxx)
Date: Thu Nov 11 1999 - 12:39:52 GMT-3
Howard,
Ben is right. You have 2 paths to the destination 172.16.2.1. It appears that
they are load balancing, on a per-packet basis. The "ip route-cache" statement
will then do load balancing on a per destination basis, meaning all packets to
172.16.2.1 will go through one link only.
Now, here is more info on why you see the trace route going through different
links. The default for trace route is to send 3 probes. An extended trace
will allow you to choose a different number, if you wish, but it is not
important. So, as you are doing load balancing on a per-packet basis (no ip
route-cache), one probe goes through one link #1, the next probe through link
#2, the third probe goes through link #1, etc. Note that this is not a problem,
it is the default behaviour, and what is expected with per-packet load
balancing.
Hope this helps.
Brian Hanson
Ben Rife wrote:
> Make sure you don't have the statement "no ip route-cache" on your router's
> serial interfaces. If it is configured, it will round-robin switch packets
> over the available paths to the destination when there are multiple paths,
> independent of the routing protocol, I believe. I have had this problem in
> the past as well. Let me know if this helps.
>
> (26 days)
>
> Ben
>
> ----- Original Message -----
> From: Rahmlow, Howard F. <howard.rahmlow@unisys.com>
> To: <ccielab@groupstudy.com>
> Sent: Tuesday, November 09, 1999 10:24 AM
> Subject: Frame Relay and Trace Route
>
> > I'm using a 4500 router as a Frame switch, with 3 routers as end points.
> The
> > Frame is fully meshed. Using the setup very close to Caslow pg 138.
> > Everything works fine, I can ping all the ip address, and telnet from one
> > router to the next with no problems. When I do a trace route, if the
> address
> > is not a connected router. The trace seems to bounce around.
> >
> > Example
> > R2501#show ip route
> > Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
> > D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
> > N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
> > E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
> > i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate
> > default
> > U - per-user static route, o - ODR
> >
> > Gateway of last resort is not set
> >
> > 172.16.0.0/24 is subnetted, 3 subnets
> > C 172.16.1.0 is directly connected, Serial1.2
> > O 172.16.2.0 [110/128] via 172.16.1.2, 3d19h, Serial1.2
> > [110/128] via 172.16.3.2, 3d19h, Serial1.3
> > C 172.16.3.0 is directly connected, Serial1.3
> > R2501#trace 172.16.2.1
> >
> > Type escape sequence to abort.
> > Tracing the route to 172.16.2.1
> >
> > 1 172.16.3.2 4 msec
> > 172.16.1.2 8 msec
> > 172.16.3.2 8 msec
> > R2501#
> >
> >
> > As you can see it goes to 172.16.3.2, then to 172.16.1.2, then back to
> > 172.16.3.2
> >
> > Any ideas, am I missing something, I don't think its normal. I get the
> same
> > resault with OSPF, RIP, EIGRP ect..I also have reloaded all the routers a
> > few times, and get the same thing.
> >
> > Thanks
> > Howard
> >
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