03-31-2010 10:42 PM - edited 03-06-2019 10:25 AM
Hi guys, I am running a lab through dynamips using isis. I have a router R5(L1 router) which is connected to R6(lL1-L2 router). R6 is connected with other L1-L2 routers. I tried to change the ATT-bit when R6 sends LSP-L1 tou R5 when the backbone area is down but unfortunately is not working. I tried when the backbone area is down R6 not to advertise LSPs with the ATT bit attached (wich means set to zero(o)) that way no default-route route will appear on the R5 router. I follow the instructions on the following url; http://www.cisco.com/en/US/products/ps6599/products_white_paper09186a00804fa7a0.shtml " using IS-IS ATT-bit Control Feature" quick explanation; I used clns filter-set to match the backbone area which was 49.0002 example: clns filter-set match-49.0002-area permit 49.0002 then I used a route-map to match the clns filter name router-map is-match-49.0002-area permit 10 match clns address match-49.0002 and then under the router config on R6 router isis . set-attached-bit route-map is-match-49.0002-area I am not sure if I am missing anything but when I turn off all the L1-L2 routers except R6 then R6 kept sending LSPs with the att-bit set to 1 and a default route on R5 is pointing to R6 even if the backbone area was down. Can you please advice? Many thanks, Spyros * I am using IOS version12.2(25)s15
Solved! Go to Solution.
04-01-2010 06:01 AM
Hello Spyros,
I guessed it was for your studies, however it can be an interesting feature.
For IP there is an additional tool a default route 0.0.0.0/0
see this taken from our production network:
RT-TO-CRN-P1-E-1#sh isis database | inc 1/0/0
RT-TO-CRN-SM-E.00-00 0x00004CA7 0x34AB 51626 1/0/0 (2)
RT-TO-CRN-SM-E.00-00 0x00003C3B 0xBA80 51626 1/0/0 (10)
RT-TO-CRN-SF-E.00-00 0x0000D013 0x3D06 43249 1/0/0 (18)
RT-TO-CRN-SF-E.00-00 0x0000CFDB 0xE619 47459 1/0/0 (19)
RT-TO-CRN-P1-E-1#
only the first two nodes are the real exit points to core for IP traffic and are the only ones to inject a default route received from core
sh ip route 0.0.0.0
Routing entry for 0.0.0.0/0, supernet
Known via "isis", distance 115, metric 100, candidate default path, type level-1
Redistributing via isis
Last update from 10.55.130.6 on GigabitEthernet3/47, 7w0d ago
Routing Descriptor Blocks:
* 10.55.130.6, from 10.80.34.2, via GigabitEthernet3/47
Route metric is 100, traffic share count is 1
10.55.130.2, from 10.80.34.1, via GigabitEthernet1/24
Route metric is 100, traffic share count is 1
in this sense the ATT bit importance is reduced when routing IP
Hope to help
Giuseppe
04-01-2010 03:31 AM
Hello Spyros,
the IOS image you are using may be not supporting this specific feature.
at the end of the document you have linked:
Cisco IOS Software Release 12.2(4)T
and you have IOS version12.2(25)s15
also if you are going to use ISIS to route IP traffic the ATT is of less importance.
Edit:
looking on the document:
>>Thus, we cannot just use the 39.0000 area address to satisfy the route map because the Layer 1/Layer 2 routers will still have the 39.0000 area address in their routing tables. Instead, we can create another area address in the backbone area as a "beacon" area address and use it to satisfy the route map
you need to deploy a second CLNS net between two other L2 routers when this net is missing on the ISIS database then the ATT bit will be cleared on L1/L2 routers that check for the presence of the beacon area-id.
The support of multiple nets is used here not for a migration but for providing a CLNS address to be checked.
Hope to help
Giuseppe
04-01-2010 05:47 AM
Hi Giuseppe, first of all thank you very much for your answer. To be honest I didn't mention that the ATT-bit control feature is not supported it on the IOS that I am currently running. Unfortunately I am going through my CCIE studies for the SP and I am testing almost everything just to fill confident before I go ahead with anything else. I am not sure why you say the following and if you can explain further that will be grade; "also if you are going to use ISIS to route IP traffic the ATT is of less importance." I think the ATT-bit on the LSPs is important cause the L1 routers have no other way other than that to route traffic to the other areas on to the other part of the is-is domain. The L1-L2 router get the responcibility through the ATT bit to add a default route on the L1's routing table. Without that you have to add a static route manually on the L1 router or you have to use route-leaking if you want to learn other routes other than this particular L1 router. Of cource route-leaking is for resolving suboptimal routing and not for that issue in most cases If you can explain further that will be grade. Many thanks, Spyros
04-01-2010 06:01 AM
Hello Spyros,
I guessed it was for your studies, however it can be an interesting feature.
For IP there is an additional tool a default route 0.0.0.0/0
see this taken from our production network:
RT-TO-CRN-P1-E-1#sh isis database | inc 1/0/0
RT-TO-CRN-SM-E.00-00 0x00004CA7 0x34AB 51626 1/0/0 (2)
RT-TO-CRN-SM-E.00-00 0x00003C3B 0xBA80 51626 1/0/0 (10)
RT-TO-CRN-SF-E.00-00 0x0000D013 0x3D06 43249 1/0/0 (18)
RT-TO-CRN-SF-E.00-00 0x0000CFDB 0xE619 47459 1/0/0 (19)
RT-TO-CRN-P1-E-1#
only the first two nodes are the real exit points to core for IP traffic and are the only ones to inject a default route received from core
sh ip route 0.0.0.0
Routing entry for 0.0.0.0/0, supernet
Known via "isis", distance 115, metric 100, candidate default path, type level-1
Redistributing via isis
Last update from 10.55.130.6 on GigabitEthernet3/47, 7w0d ago
Routing Descriptor Blocks:
* 10.55.130.6, from 10.80.34.2, via GigabitEthernet3/47
Route metric is 100, traffic share count is 1
10.55.130.2, from 10.80.34.1, via GigabitEthernet1/24
Route metric is 100, traffic share count is 1
in this sense the ATT bit importance is reduced when routing IP
Hope to help
Giuseppe
04-01-2010 09:34 AM
Hi Guiseppe,
thanks for the extra information. The default route is quit interested.
I assume that the default route is getting the priority because of the admin distance. I hope I am correct.
You will find me asking more questions in the future generally.
I am almost at the end of routing for my studies and I will try to refresh everything and go back to what I left which I couldn't understand.
So you will find me asking more questions please advice if you are familiar with any!
I started the studies and I am walking completely alone so the only place I can discuss anything is through that forum whcih I am new.
Once more,
Many thanks,
Spyros
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