RE: [Isis-wg] Computation of areas in MT-ISIS

["Pudiyapura, Ajeer" <[e-mail]>]

Naiming,

   Please consider the following MT-ISIS network example:


		      N3(L2-only)
		     /  \
		    /    \
 		 V6/      \V6
		  /        \
		 /          \
	(L1L2)N2 -------- N4(L1L2)
		|	V4     |  
		|	       |
	 V4/V6|	  	 | V4/V6
	      |		 |
	  	N1(L1)	N5(L1)

Area Configurations:

 N1: A1
 N2: A1, A2
 N4: A2, A3
 N5: A3

The default (IPv4) Topology of the above network would be:

		      
	(L1L2)N2 -------- N4(L1L2)
		|	       |  
		|	       |
	      |            |
	      |		 |
		N1(L1)	N5(L1)


Here:
1. Each adjacent router is configured with at least one common area id,
hence forming an L1 adjacency.
2. Both N2 and N4 computes Union Area Address set, which would be
{A1,A2,A3}
3. Neither N2 nor N4 would set the attached bit in L1 LSP since the
entire network acts as an L1 cloud.
4. Neither N1 nor N5 would install a default route.
5. Since N1 would get L1 LSP from N5 and vice versa, routing between
them would work fine, as expected.


 Now please consider the IPv6 Topology of the above network:


		      N3(L2-only)
		     /  \
		    /    \
 		   /      \
		  /        \
		 /          \
	(L1L2)N2 		N4(L1L2)
		|	       |  
		|	       |
	      |	  	 | 
	      |		 |
	  	N1(L1)	N5(L1)


6. Since both N2 and N4 would use the Union Area Address set from
Default topology, it will be {A1,A2,A3} as in step 2 above.
7. Neither N2 nor N4 would set the attached bit in their L1 LSPs because
no more Areas are reachable through L2 routing than the Union Area
Address set. 
8. Neither N1 nor N5 would install a default route.
9. Since N1 in this case would not get L1 LSPs from N5 (and vice versa)
routing will not be available between N1 and N5, even though there is a
path between them that uses the L2 connectivity.  

Please correct me if I am wrong.
Thanks
-Ajeer Pudiyapura


-----Original Message-----
From: Naiming Shen [mailto:[e-mail]] 
Sent: Monday, October 10, 2005 11:34 AM
To: May Lu
Cc: Pudiyapura, Ajeer; [e-mail]
Subject: Re: [Isis-wg] Computation of areas in MT-ISIS

May,

May Lu said the following on 10/10/2005 09:20 AM:
> If a MT-ISIS node runs different protocols on its interfaces, how
> does the node broadcast its union address in L2 LSP?
> 
> See configuration below:
> 
> Node1(area 01, 04) ----  Node2 (area 01, 02) --- Node3 (area 02, 05) 
> IP                               Ipv6
> 
> All three nodes are MT-ISIS nodes. Node2 is connected to Node1 with
> IP protocol. Node2 and Node3 are connected with IPV6 protocol. Node2
> IP union addresses should be 01, 02 and 04. Node2 Ipv6 union
> addresses should be 01, 02 and 05. Is this correct?
> 
> If the union address does not consider the protocol, in the following
> case, there is a problem:
> 
> Node1 (area 01)  ------ Node2 (area 01) ----- Node3 (area 01, 02) IP
> Ipv6 All three nodes are MT-ISIS nodes. Node1 and Node2 are connected
> via IP protocol. Node2 and Node3 are connected via Ipv6 protocol.
> Node1 is a level1 only node. Node2's union addresses are 01 and 02.
> Node2 will set attached bit on IP protocol and Node1 will set the IP
> default route towards Node2. Actually Node1 and Node2 are using the
> same area address in IP network and Node1 shouldn't set default route
> to Node2.
> 

But don't you already have problem even if Node3 is IP(not IPv6) ?
or do we already have problem if they are not MT-ISIS nodes?  If we
are playing with IP/IPv6, why should we assigning different areas to
those nodes ?

thanks.
- Naiming

> Thanks, - Xiaomei Lu
> 
> 
> -----Original Message----- From: 	Naiming Shen
> [mailto:[e-mail]] Sent:	Saturday, October 08, 2005 12:01
AM 
> To:	Pudiyapura, Ajeer Cc:	[e-mail] Subject:	Re:
[Isis-wg]
> Computation of areas in MT-ISIS
> 
> 
> 
> Pudiyapura, Ajeer said the following on 10/06/2005 11:09 AM:
> 
>> Hi.
>> 
>> 
>> 
>> I have the following questions:
>> 
>> 
>> 
>> 1)       How is Area Address Computation (section 7.2.11 of ISO/IEC
>>  10589) done in Multi Topology IS-IS? Are they computed separately
>> for each topology?
>> 
> 
> 
> No. MT-ISIS node keeps the same system-id, areas, levels, hostname, 
> etc. there is no change to any of that.
> 
> thanks. - Naiming
> 
> 
>> 2)       If so, how is the resulting set advertised in L2 LSPs
>> since there is no mechanism to do this per topology?
>> 
>> 
>> 
>> Thanks
>> 
>> -Ajeer Pudiyapura
>> 
>> 
>> 
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