draft-ietf-idr-restart-01.txt   draft-ietf-idr-restart-02.txt 
Network Working Group Srihari Ramachandra (Procket Networks) Network Working Group Srihari Ramachandra (Procket Networks)
Internet Draft Yakov Rekhter (Juniper Networks) Internet Draft Yakov Rekhter (Juniper Networks)
Expiration Date: January 2002 Rex Fernando (Procket Networks) Expiration Date: July 2002 Rex Fernando (Procket Networks)
John G. Scudder (Cisco Systems) John G. Scudder (Cisco Systems)
Enke Chen (Redback Networks) Enke Chen (Redback Networks)
Graceful Restart Mechanism for BGP Graceful Restart Mechanism for BGP
draft-ietf-idr-restart-01.txt draft-ietf-idr-restart-02.txt
1. Status of this Memo 1. Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
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The most significant bit is defined as the Forwarding State The most significant bit is defined as the Forwarding State
bit which can be used to indicate if the forwarding state for bit which can be used to indicate if the forwarding state for
the <AFI, Sub-AFI> has indeed been preserved during the previous the <AFI, Sub-AFI> has indeed been preserved during the previous
BGP restart. When set (value 1), the bit indicates that the BGP restart. When set (value 1), the bit indicates that the
forwarding state has been preserved. forwarding state has been preserved.
The remaining bits are reserved. The remaining bits are reserved.
The advertisement of this capability by a BGP speaker also implies The advertisement of this capability by a BGP speaker also implies
that it will generate the End-of-RIB marker upon completion of its that it will generate the End-of-RIB marker (for all address families
initial routing update to its peer. The value of the "Restart Time" exchanged) upon completion of its initial routing update to its peer.
field is irrelevant in the case that the capability does not carry The value of the "Restart Time" field is irrelevant in the case that
any <AFI, Sub-AFI>. the capability does not carry any <AFI, Sub-AFI>.
6. Operation 6. Operation
A BGP speaker may advertise the Graceful Restart Capability for an A BGP speaker may advertise the Graceful Restart Capability for an
address family to its peer only if it has the ability to preserve its address family to its peer only if it has the ability to preserve its
forwarding state for the address family when BGP restarts. forwarding state for the address family when BGP restarts.
Even if the speaker does not have the ability to preserve its Even if the speaker does not have the ability to preserve its
forwarding state for any address family during BGP restart, it is forwarding state for any address family during BGP restart, it is
still recommended that the speaker advertise the Graceful Restart still recommended that the speaker advertise the Graceful Restart
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of the OPEN message. Unless allowed via configuration, the of the OPEN message. Unless allowed via configuration, the
"Forwarding State" bit for an address family in the capability can be "Forwarding State" bit for an address family in the capability can be
set only if the forwarding state has indeed been preserved for that set only if the forwarding state has indeed been preserved for that
address family during the restart. address family during the restart.
Once the session between the Restarting Speaker and the Receiving Once the session between the Restarting Speaker and the Receiving
Speaker is re-established, the Restarting Speaker will receive and Speaker is re-established, the Restarting Speaker will receive and
process BGP messages from its peers. However, it shall defer route process BGP messages from its peers. However, it shall defer route
selection for an address family until it receives the End-of-RIB selection for an address family until it receives the End-of-RIB
marker from all its peers (excluding the ones with the "Restart marker from all its peers (excluding the ones with the "Restart
State" bit set in the received capability). It is noted that prior to State" bit set in the received capability and excluding the ones
route selection, the speaker has no routes to advertise to its peers which do not advertise the graceful restart capability). It is noted
and no routes to update the forwarding state. that prior to route selection, the speaker has no routes to advertise
to its peers and no routes to update the forwarding state.
In situations where both IGP and BGP have restarted, it might be In situations where both IGP and BGP have restarted, it might be
advantageous to wait for IGP to converge before the BGP speaker advantageous to wait for IGP to converge before the BGP speaker
performs route selection. performs route selection.
After the BGP speaker performs route selection, the forwarding state After the BGP speaker performs route selection, the forwarding state
of the speaker shall be updated and any previously marked stale of the speaker shall be updated and any previously marked stale
information shall be removed. The Adj-RIB-Out can then be advertised information shall be removed. The Adj-RIB-Out can then be advertised
to its peers. Once the initial update is complete for an address to its peers. Once the initial update is complete for an address
family (including the case that there is no routing update to send), family (including the case that there is no routing update to send),
 End of changes. 

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