On Tue, 7 Nov 2000, Phil Barker wrote:
> Hi Gang,
> Three Routers in a triangle. Labelled Top, Left
> and Right. Serial Connections between Top -> Left, and
> Top -> Right. Ethernet connection between Left and
> Right. Sniffer placed on Ethernet segment.
>
> The Top Router has 2 routes to the Ethernet segment
> and is Load Balancing.
> The Right Router is my problem. It only learns one
> route to the network TOP->Left via the Serial Route,
> why doesn't it learn this network via the Ethernet
> Segment also ?
>
> Sniffer can see the network Top->left being advertised
> by the Router left. debug on Router Right reveals
> supressing Null Update ???
>
> When I cut the link Top-Right the Network Top->Left is
> eventually flushed out ???
split horizon. Imagine this:
Top
Left Right
TOP learns LEFT from LEFT.
RIGHT learns TOP from TOP.
RIGHT learns LEFT from TOP.
RIGHT announces routes about TOP and LEFT to LEFT!!!
LEFT will not announce routes about either TOP or LEFT
out its Left/Right interface, since it heard about it
from there.
that might not be the *exact* sequence of the loop you are seeing, but
"supressing null route" is a split horizon error. I have seen this for
example when configuring a static SAP on the same interface you wish to
announce it on.........split horizon will kick in, and you will see
"supressing null route".
You have created a loop by design above. Split horizon's job is to break
it at some point, which its done between Left and Right.
Brian
>
> I'm baffled,
>
> Can anyone help out ?
>
> Regards,
>
> Phil.
>
>
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-----------------------------------------------
Brian Feeny, CCNP, CCDP [EMAIL PROTECTED]
Network Administrator
ShreveNet Inc. (ASN 11881)
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