From: damien (damien@xxxxxxxxxxx)
Date: Sun Aug 06 2000 - 14:57:51 GMT-3
Remember the Syncronization is the de-facto operation, Cisco add in
the no-sync.........it quite simply states that routes learned vi IBGP
are ADVERTISED irrespective of an IGP route been
known.............therefore this invalidates the decision step 1
process in defacto-BGP......
Remember BGP has nothing to do with adding the Route into Main Routing
Table only the BGP RIB. It is the Routing Process not the Protocol
that determines whether the Route is added to the main Routing Table.
BGP just decides whether to add it to the BGP RIB. If the next hop is
inaccessable, do not add to the BGP RIB, if no sync is enabled, ignore
this first decision step. At this point if the Route is in the BGP
RIB. The Routing Process will add the entry to the main FIB assuming
there is not a same route with a lower admin distance......
thats my 2p............
----- Original Message -----
From: John Conzone
To: damien
Cc: ccielab
Sent: Sunday, August 06, 2000 4:29 PM
Subject: Re: Whats wrong with this picture (Sho ip BGP and Sho ip
route)
Well, here's the rub. What does synchronzation do?
My reading suggests that synchronization means that if an IBGP
speaker receives a route rom another IBGP speaker, he will not
advertise that route to another EBGP speaker (transit AS) until that
route is in the route table (by IGP, static, etc.) This to prevent non
bgp speaking routers within that AS from dropping a packet with a
destination they do not know about as it goes from one IBGP per to
another as it transits the AS.
My understanding of next hop is different. My read is that if an
IBGP speaker receives a route from another IBGP speaker, and the next
hop on that advertisement is not known to the recieving router, he
will not install it in his routing table. Synchronization, from my
reading and lab work, does not affect the next hop rule.
If I am mistaken someone please correct me. If correct, my router
should not be installing the route, because he does not know how to
get to 137.20.20.1.
----- Original Message -----
From: damien
To: John Conzone
Sent: Sunday, August 06, 2000 1:12 PM
Subject: Re: Whats wrong with this picture (Sho ip BGP and Sho ip
route)
I am assuming you have no sync enabled......you have no route to the
next hop....if sync was enabled that should not be the case.....its a
bit hard without looking at the configs..........
----- Original Message -----
From: John Conzone
To: ccielab
Sent: Friday, August 04, 2000 12:11 AM
Subject: Whats wrong with this picture (Sho ip BGP and Sho ip route)
Please take a look at the following "sho ip bgp" and "sho ip
route" and tell me what is wrong with this picture, and why this is
happening? According to page 149 of Halabi's book, this shouldn't be.
(Hint: R1 can't ping 137.20.20.1)
r1#sho ip bgp
BGP table version is 2, local router ID is 200.200.200.1
Status codes: s suppressed, d damped, h history, * valid, > best, i -
internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*>i192.168.60.0 137.20.20.1 20 100 0 1 i
r1#sho ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B -
BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS
inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is 24.2.28.1 to network 0.0.0.0
C 200.200.200.0/24 is directly connected, Loopback0
B 192.168.60.0/24 [200/20] via 137.20.20.1, 00:05:08
172.168.0.0/24 is subnetted, 1 subnets
C 172.168.21.0 is directly connected, Serial0
24.0.0.0/24 is subnetted, 1 subnets
C 24.2.28.0 is directly connected, Ethernet0
C 192.168.17.0/24 is directly connected, Serial1
S* 0.0.0.0/0 [1/0] via 24.2.28.1
r1#
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