isis area migration

[gdy1039]

Hello

I am learning on lab. Would you please help my below 2 question.

Q1. Why I don't get L1L2 connection type between R3 and R4?

Q2. Should I suppose no down because of I have 2 area address connection after I remove one of it?

Thanks for your time.

R3 E0/0  --    E01 R4

[Harold Ritter]

Hi @gdy1039 ,

Q1. You need to configure the same area address on both router to establish a L1L2 adjacency.

Q2. The Net ID change causes the adjacency to be reset.

BTW, the multi area feature purpose is not to perform migration. For more information about this feature, please refer to the following document.

https://content.cisco.com/chapter.sjs?uri=/searchable/chapter/content/en/us/td/docs/ios-xml/ios/iproute_isis/configuration/xe-3e/irs-xe-3e-book/irs-ma-sprt.html.xml

Regards,

[gdy1039]

Dear Harold Ritter

Thank you very much for your reply.

I completely understand about Q1 now. Thank you.

Would you mind answer my below new question to help me understand that link?

Q1. under interface, what's different between "clns router isis" and "router isis"?

Q2. key command "partition avoidance",   I had read command reference still not understand. Try to ask in other way, if not have this command, what bad thing will happen?

To cause an Intermediate System-to-Intermediate System (IS-IS) Level 1-2 border router to stop advertising the Level 1 area prefix into the Level 2 backbone when full connectivity is lost between the border router, all adjacent Level 1 routers, and end hosts, use the partition avoidance command in router configuration mode.

Q3. ADI starting with 49 is private addresses. But 47 represent ISO international code dsignator means I should use it at what environment or situation?

Thanks for your valuable time.

Best Regards.

Scott Gao

[Georg Pauwen]

Hello,

to answer your question about partition avoidance, I have done some research, and I think that this is a feature that is not actually implemented by Cisco (or any other vendors).

If you look at the output below, the fields marked in bold represent the 'Partition Repair' bit, which is always zero, meaning it is not set regardless of configuring 'partition avoidance' under the ISIS router process or not:

IS-IS Level-1 Link State Database:
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
R1.00-00 * 0x0000000F 0xE8A3 1034 1/0/0
R2.00-00 0x0000000B 0xF76D 1028 0/0/0
R2.01-00 0x00000006 0x74D7 1028 0/0/0
IS-IS Level-2 Link State Database:
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
R1.00-00 * 0x00000014 0x5E4B 1040 0/0/0

[gdy1039]

Hello Georg

Thanks for reply.

I think If lsp had not been partition, P not set to 1 is normal.

I also make a test, inject 500 loopback IP to LSP, then if split to 5 LSP which are from R1.00-00 TO R1.00-04. But P bit still not set to 1.

I ask this topic because of I am reading book "Routing TCP/IP Volume I second Edition", Which written by Jeff Doyle and Jennifer Carroll. Chapter 10 for ISIS talking this. So I think it should can work on Cisco.

Section 10.2.3 is Example area migration. Change area from A to B without drop adjacency.

Thank you

Best Regards.

[Harold Ritter · Accepted solution]

Hi @gdy1039 ,

Q1. ISIS supports both CLNS and IP. "clns router isis"  is for CLNS routing and "ip router isis" for IP routing.

Q2. As far as I know, partition avoidance is only for CLNS routing and will stop advertising the L1 area into L2 area, even though it is locally configured, if the router loses connectivity to the L1 area.

Just to clear the confusion, here's an excerpt from an internal document clarifying the difference between "partition avoidance" and "partition repair":

"Partition Avoidance is not the same as Partition Repair. Partition repair is an optional feature from the ISIS specification ISO 10589. When an area 1 becomes partitioned, it could be repaired through the use of the L2 paths. The P-bit in the LSP header indicates the support for Partition Repair. Cisco routers do not support Partition Repair; they never set the P-bit and ignore this bit. This L1 repair path through the L2 is a virtual link where the L1 packets are encapsulated with source and destination addresses being the partition designated L2 ISs. "

Q3. I have seen both being used in production networks, although I personally prefer the private (49).

Regards,

[gdy1039]

Hello Ritter

Thank you very much for your help.

I don't fully understand. Maybe I lean more then come back to understand.

Thank you.

Best Regards.

Scott Gao