Subject: [Isis-wg] Reg: Over Load bit

From: "Rayapureddi Ramesh" <[email-masked]>
Date: Mon, 6 Aug 2001 18:07:20 +0530

Hi,

ISO/IEC FCD 10589 ISIS Standardis saying that "As a result of network
misconfiguration, or certain transitory conditions, it is possible that
there may be insufficient resources available to store the a received Link
State PDU. When this occurs, an IS needs to take certain steps to ensure
that if its LSP database becomes inconsistent with other IS's, that these
ISs do not rely on forwarding paths through the overloaded IS". 

Take an example..
   
              R1-----------------R2--------------------R3
                                    |                       |
                                    |                       |
                                    |                       |
                                    R4------------------R5

Here R1 forward to R2 if any packet destined to routers R3, R4 and R5  by
considering the forwarding path through R2 (i.e since R1 have route to R3,
R4 and R5 with R2 as next hop).
 
If R2 advertises an LSP with Overload Bit set, then R1 should not forward to
R2 if any packet destined to R3, R4 and R5 since here R1 will not consider
forwarding path through R2 (i.e it will not install routes to R3, R4 and R5
with next hop as R2).

Am I correct?.

Here my doubt is---- 
will this applicable to IP information (in LSP packet) also OR only to OSI
information only while processing the LSPs received from overloaded IS?.

Please clarify doubt.

Regards,
Ramesh

---

From: stefano previdi <[email-masked]>
Date: Mon, 06 Aug 2001 15:09:10 +0200

>forwarding path through R2 (i.e it will not install routes to R3, R4 and R5

yes.

>information only while processing the LSPs received from overloaded IS?.

When running SPF, you don't move into the TENT list the neighbors
of a node if such node has the overload-bit set. Therefore you
won't continue to build the sub-tree after the overload-bit-node.
This means that any route advertised by nodes downstream to the
overload-bit-node will simply be never calculated, no matter their
address family.

s.

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