Comments inline...
~-----Original Message-----
~From: Naidu, Venkata [mailto:Venkata.Naidu@Marconi.com]
~Sent: Wednesday, April 25, 2001 11:40 AM
~To: juniper-nsp@puck.nether.net
~Subject: RE: [j-nsp] isis question
~
~
~Hi Chris
~
~I had this question for a long...
~* If IS-IS is not using any L3 (CLNP/IP) then
~ those IS-IS routing packets can't be forwarded beyond
~ 1 hope. For example, OSPF packets can be forwarded
~ or flooded more than 1 hope in Virtual neighbor
~ environment. Am I correct or missing something?
This is correct.
~* If IS-IS packets are forwarded directly over L2
~ then how does it cope up with fragmentation and
~ reassembly services. I am not able to visualize
~ how IS-IS packets will be transmitted over different
~ L2 technologies like ATM and broadcast/multicast capable
~ networks etc. How they get code-points?
This is really answered in two ways.
IS-IS PDUs can be fragmented, as the maximum LSP is 65535 bytes. (There are
ways of extending this in the works). As such, an LSP is built by an IS,
and fragmented as needed so that it does not exceed the max SNPDU size.
However, this is only done at the originating router. This means that there
needs to be consistency on the IS-IS MTU size throughout the internetwork.
The second point to make is that IIH PDUs are padded to maxsize - 1 octets.
This ensures that mismatched MTUs on interfaces do not cause fragmentation
issues.
It should be noted that Cisco allows you to set the max-lsp size in the
router configuration. In JUNOS, you have to set the lsp-size on the media
itself, or use groups to set it globally on the router. Unless someone
knows something else?
regards,
chris
Thanks & Regards --
http://www.geocities.com/kvsnaidu
-----Original Message-----
From: Chris Flores [mailto:chris.flores@onfiber.com]
Sent: Wednesday, April 25, 2001 10:59 AM
To: 'zheng jiang gu'; mpls-ops@mplsrc.com; juniper-nsp@puck.nether.net;
Aviva Garrett
Subject: RE: [j-nsp] isis question
My response is in-line. I hope it helps...
-----Original Message-----
From: zheng jiang gu [mailto:zjgu@ce-air.com]
Sent: Tuesday, April 24, 2001 9:15 PM
To: mpls-ops@mplsrc.com; juniper-nsp@puck.nether.net; Aviva Garrett
Subject: [j-nsp] isis question
hi all:
When I study isis, I meet the problem:
1 Which network layer use to encapsulation isis-pdu?
Is it clnp or ip?
CF: The OSI packets (or PDUs) are forwarded "as is" or transmitted directly
over the underlying link layer without the need for encapsulation - per RFC
1195.
2 How many IS-IS adjacency between point-to-point routers?
CF: IIH (IS-IS Hello) PDUs are utilized to initialize and maintain
adjacencies between neighbors. On a p2p link, one neighbor creates one
adjacency. Do you have a more specific question that needs answering?
br
shawn
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