From: Peter van Oene (pvo@usermail.com)
Date: Tue Mar 04 2003 - 14:23:00 GMT-3
At 06:24 PM 3/3/2003 +0100, octavio@sztele.com wrote:
>Hi
>
>I4m working with ISIS for the first time. I4m reading the Doyle book but
>something seem not to work in the way it is said:
>
>- It is said, CLNS routing must be enabled and because routers use CLNS
>PDUs instead of IP packet to do adyacencies, it could be possible routers
>with different IP address to become adyacents.
CLNS routing is not required. It is also possible for ISIS routers to form
an adjacency without direct IP connectivity.
>I have seen it is not necesary to enable CLNS routing to do ISIS (only for
>IP) works. And then, without CLNS routing, routers in different networks
>dont became adyacents.
CLNS routing or otherwise has no impact on adjacency formation. In
general, L1 routers form L1 adjacencies when they have at least one area-id
in common, and L2 routers form L2 adjacencies with other L2 routers,
irrespective of area-id.
>- It is said IP process can not directly interpret the ATT bit. It is
>necesary to enable ISIS for CLNS on the interfaces in adition to ISIS for
>IP. In this way, L1 routers have a default route to the L1/l2 router.
>But I have seen it is not necesay. If we disable CLNS routing the L1
>routers see ATT=1 and install a default route to the L1L2 router.
I am not aware of any CLNS depencies on ATT bit processing. You should not
need to turn on CLNS globally, or interface-local for ATT to be process
correctly.
>- It is said too, you can configure a default route 0.0.0.0/0 on L1/L2
>routers and do ISIS to advertise it with the command (default-information
>originate) to the L1 routers inside the area. But in this way, the default
>route is advertise only inside the L2 LSPs and then the L1 routers dont see
>the default route.
L1 routers set their own default route which likely supercedes any learned
routes. This is normal behavior and likely explains what you are
seeing. I would need to check and see if 0/0 can be advertised in an L1
LSP via redistribution. There is no technical reason why it could not from
what I understand. However, I do expect the routers to make their own
default route selection based upon closest L1L2 router and I'd expect this
route to supercede anything recieved in a 130/135 TLV.
Pete
>Thanks
>Octavio
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