深入浅出REST

BGP router origin :
1 netwrok statement

netwrok <net>mask <mask> origin internal (IGP)
nework <net> backdoor
set AD 200 for ebgp rotue,but do not originate (the same prefix)
takes precedence over redistribution (the same prefix)

it auto-summary is enable and default classful mask is ued(mask not defined) the any smaller prefix inject that classful ALONG WITH THOSE TRIGGERING SUBNETS .

2 default-route

network 0.0.0.0 (must have 0/0 in routing table)
by default not redistributed from other protocols with any outbound filters(prefix-list ,route-map ,filter-list).the default-information originate
must be used
neighbor <ip > default-originate
originate even if 0/0 not in bgp table (unless route-map is used and 0/0 is checked)

3 redistribution
if auto-summary is enable then any smaller prefix redistributed will inject classful route ONLY .
takes precedence over aggregation
origin incomliete
bgp redistribute-internal
bgp prefixes are not redistributed into IGP by default even if redistributed is configured .

BPG CONVERGENCE:
1 NEXT-HOP TRACKING
enable by default
bgp nexthop trigger enbale
show ip bgp attr nexthop
show ip bgp attr nexthop ribfilter
bgp nexthop trigger delay <0~100 >
bgp waits 5 seconds beform triggering NHT scan

2 FAST SESSION DEACTIVATION
if we lose our router to the peer ,tear down the session .
no need to wait for the hold timer to expire
neighbor <IP> fall-over
no bgp fast-external-fallover
does not react to connected interface going down ,waits for holdtime

3 READ-ONLY MODE
bgp update-delay <sec>
router is in read-only mode (no update sent)untill
timeout expires of first keeplive is received

4 IGP startup
ISIS
set overload-bit on-startup wait-for-bgp
if not signalled in 10min,OL bit is removed
OSPF
max-metric router-lsa on-startup wait-for-bgp
if not signalled in 10min ,max OSPF cost is removed

5 NSF:
bgp graceful-restart
graceful restart capability in exchange in open message
neighbor<ip>ha-mode graceful-restart
FIB is marked as stale

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