[OSPF] Stub areas and type 4 summary LSAs
RAMAKRISHNADTV <RAMAKRISHNADTV@infosys.com> Fri, 20 September 2013 07:03 UTC
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From: RAMAKRISHNADTV <RAMAKRISHNADTV@infosys.com>
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Thread-Topic: Stub areas and type 4 summary LSAs
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Date: Fri, 20 Sep 2013 07:03:45 +0000
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Subject: [OSPF] Stub areas and type 4 summary LSAs
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Hi, Could you please clarify the following point in OSPFv2 (RFC 2328) w.r.t stub areas? The following is excerpted from Section 10.6 (Receiving Database Description Packets): When the router accepts a received Database Description Packet as the next in sequence the packet contents are processed as follows. For each LSA listed, the LSA's LS type is checked for validity. If the LS type is unknown (e.g., not one of the LS types 1-5 defined by this specification), or if this is an AS- external-LSA (LS type = 5) and the neighbor is associated with a stub area, generate the neighbor event SeqNumberMismatch and stop processing the packet. Otherwise, the router looks up the LSA in its database to see whether it also has an instance of ... This is correctly saying that stub areas should not process external LSAs (LS type 5). But what about type 4 summary LSAs (related to ASBR)? As far as I understand, stub areas should not receive these LSAs. But this paragraph is not explicit about it. I believe this paragraph needs to be updated to indicate that received type 4 summary LSAs and type 5 external LSAs should elicit the same behavior in stub areas: generate the neighbor event SeqNumberMismatch and stop processing the packet. On the other hand, originating LSA side description in RFC correctly states as follows. >From Section 12.4.3 (Summary-LSAs): ...If so, a Type 4 summary-LSA is originated for the destination, with Link State ID equal to the AS boundary router's Router ID and metric equal to the routing table entry's cost. Note: these LSAs should not be generated if Area A has been configured as a stub area.... Regards, Ramakrishna DTV. **************** CAUTION - Disclaimer ***************** This e-mail contains PRIVILEGED AND CONFIDENTIAL INFORMATION intended solely for the use of the addressee(s). If you are not the intended recipient, please notify the sender by e-mail and delete the original message. Further, you are not to copy, disclose, or distribute this e-mail or its contents to any other person and any such actions are unlawful. This e-mail may contain viruses. Infosys has taken every reasonable precaution to minimize this risk, but is not liable for any damage you may sustain as a result of any virus in this e-mail. You should carry out your own virus checks before opening the e-mail or attachment. Infosys reserves the right to monitor and review the content of all messages sent to or from this e-mail address. Messages sent to or from this e-mail address may be stored on the Infosys e-mail system. ***INFOSYS******** End of Disclaimer ********INFOSYS***
- [OSPF] Stub areas and type 4 summary LSAs RAMAKRISHNADTV
- Re: [OSPF] Stub areas and type 4 summary LSAs Acee Lindem