Re: [j-nsp] IS-IS L1 Internal Reachability not propogated in Level2 LSPs

From: Nischal Sheth (
Date: Thu Jun 22 2000 - 17:12:37 EDT

"Martin, Christian" wrote:
> Cisco folk, sorry for the JUNOS question here, but I know there are some of
> you lurking out there that may have an answer to this...
> It appears that, at least in JUNOS 4.0, IP Internal Reachabilty TLV data is
> not sent in L2 LSPs for subnets directly connected to the router. Here is
> the topology:
> |-----------0---------------0====================0----------------0---------
> ---|
> ^ ^ ^ ^ ^ ^ ^ ^ ^
> x.L1-PTP L1-IS y.L1 L1/L2 A.L2-PTP L1/L2 z.L1-PTP L1-IS
> k.L1-LAN
> The 0 represents an IS, and the - represents a L1 ckt, the = is L2. The
> x.L1-PTP represents subnet x, on a PTP L1 circuit.
> The leftmost L1/L2 router is an M40 running 4.0, the rest are GSRs running
> 12.0. I can see both x and y subnets throughout the area to which they
> belong, however, I cannot see y in the right L1/L2 GSR's L2 LSPDB, which
> then prevents the rest of the L2 IS's connected to it from seeing a path
> back to that area. Therefore, the L1/L2 GSR does not see y in its L2 LSPDB.
> In fact, it has no TLV 128 entries for any subnet connected to the M40, and
> no other L2 IS connected to the M40 sees the TLV. On the other hand, the
> M40 does see z in its L2 LSPDB. I suppose I could create a policy to export
> direct routes into IS-IS, but wouldn't this make them IP external? This
> changes their preference, which would break routing if there is another L2
> Cisco in the area, because it would learn about y through L1 LSPs and send
> them to other L2 routers in L2 LSPs as TLV 128 instead of 130.

You can make the M40 send y using TLV 128 if you configure IS-IS L2 to
run in passive mode on the interface in question.


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