ISIS redistribution

[Ratheesh mv]

1)May I know the difference of ISIS metric-type internal and external while redistributing ?

2)I have configured metric-type external alone without metric keyword while redistributing but it is not effecting. May I know the reason why does not ISIS set metric-type external for external routes in this situation ?

3)If I enable metric-style wide then we have TLV 135 to carry IP internal and external routes. In TLV 135 I don't see fields to mark route external while redistributing as metric-type external .In this situation how can we carry metric-type external routes?

4)Why does not ISIS show redistributed routes as external in their routing table ?

5)How can I recognize ISIS external routes in routing table ?

Thanks in advance 

[Giuseppe Larosa]

Hello @Ratheesh mv ,

in IS-IS it is more important the level the imported route will have:

if L1 the route will be exported from area by L1L2 IS node(s) in the L2 backbone.

if L2 the route is only sent out L2 links in the backbone.

We can say that for IS-IS all routes are somewhat leafs: IS-IS uses CLNP and NET entity later it has been extended to route IPv4 and to route IPv6  ( other applications exist of IS-IS for example in OTV to carry MAC addresses and in SD Access)

It is also a question of implementation in Juniper JUNOS different route prefence ( similar to Cisco AD) are used see:

https://www.juniper.net/documentation/en_US/junos/topics/reference/general/routing-protocols-default-route-preference-values.html

with higher values for external routes either L1 or L2

Edit:

see also this thread on CLN

https://learningnetwork.cisco.com/s/question/0D53i00000KssFr/isis-redistribution-gotcha-?dtid=osscdc000283

There is a relationship between internal/external and the use of wide metric. You should be able to see external routes listed with wide metric in a different TLV.

Actually TLV type 130 already means external route see

https://www.ciscolive.com/c/dam/r/ciscolive/us/docs/2019/pdf/BRKRST-2315.pdf

see slide 48, internal routes TLV 128   external routes TLV 130.

This is the reason you didn't find a route type field within TLV 130 it is implied by TLV type 130.

Hope to help

Giuseppe