04-03-2003 04:25 AM - edited 03-02-2019 06:22 AM
The BGP MED value can be received from one ebgp (AS1) peer to another ebgp (AS2) peer (say an internal IGP metric redist into AS1s bgp and accross to AS2). If the receiving AS2 peer is a transit network to AS3, crossing the ebgp peer to AS3, would the MED value remain intact, if not, what does it get set to? (is it zero? and why?).
Has anyone got some detailed information on this please?
Many thx :)
04-03-2003 05:01 AM
Hi
the med is an optional trasitive attribute and is only exchanged between ASs. A
Med Value which comes into an AS does not leave that AS again. The med value will be reseted to zero if you pass it on to an other AS (unless you set again the outgoing med).
You can find all about bgp also in the book "internet routing architectures" from
bassam halabi. I guess you would find it on the web too.
Hope that heps
Roger
04-03-2003 05:04 AM
It does help :)
many thx
04-04-2003 12:00 PM
Hello Roger,
Is there a command or method to prevent AS from reseting MED (In fact, i would like to keep my MED end to end while passing through an AS).
Best regards
04-07-2003 12:52 AM
Hi
As i stated in the posting above you have to set the med value again on the outbound interface.
That means you set the med towards an other as....the med will be o.k in this as....as soon as you send it to a third as it will be reseted...so you have to set the med again outbound towards this third as.
Hope that helps
Roger
04-07-2003 01:06 AM
This is very true and I tested it on Friday
pls look at this
RTR4 <- RTR3 <- MSFC1 <- RTR1 <- RTR2
400 eBGP 100 100 IBGP 100 100 eBGP 200 EIGRP 11
!
router eigrp 11
network 10.0.0.0
no auto-summary
no eigrp log-neighbor-changes
!
rtr2>sh ip route
10.0.0.0/8 is variably subnetted, 14 subnets, 3 masks
D 10.10.1.0/24 [90/156160] via 10.21.21.1, 17:41:30, FastEthernet0/1
D 10.10.2.0/24 [90/156160] via 10.21.21.1, 17:41:30, FastEthernet0/1
D 10.10.3.0/24 [90/156160] via 10.21.21.1, 17:41:30, FastEthernet0/1
D 10.10.4.0/24 [90/156160] via 10.21.21.1, 17:41:30, FastEthernet0/1
D 10.10.5.0/24 [90/156160] via 10.21.21.1, 17:41:30, FastEthernet0/1
C 10.10.6.0/24 is directly connected, Loopback1
C 10.10.7.0/24 is directly connected, Loopback2
C 10.10.8.0/24 is directly connected, Loopback3
C 10.10.9.0/24 is directly connected, Loopback4
D 10.2.2.0/30 [90/284160] via 10.21.21.1, 17:41:30, FastEthernet0/1
C 10.21.21.0/30 is directly connected, FastEthernet0/1
C 10.3.3.0/30 is directly connected, FastEthernet0/0
C 10.10.10.0/24 is directly connected, Loopback5
C 10.100.100.1/32 is directly connected, Loopback100
rtr2>
rtr2>sh ip bgp
% BGP not active
rtr2>
router eigrp 11
network 10.0.0.0
no auto-summary
no eigrp log-neighbor-changes
!
router bgp 200
bgp log-neighbor-changes
redistribute eigrp 11
neighbor 10.2.2.1 remote-as 100
no auto-summary
!
rtr1>sh ip route
10.0.0.0/8 is variably subnetted, 14 subnets, 3 masks
C 10.10.1.0/24 is directly connected, Loopback1
C 10.10.2.0/24 is directly connected, Loopback2
C 10.10.3.0/24 is directly connected, Loopback3
C 10.10.4.0/24 is directly connected, Loopback4
C 10.10.5.0/24 is directly connected, Loopback5
D 10.10.6.0/24 [90/156160] via 10.21.21.2, 17:42:12, FastEthernet0/1
D 10.10.7.0/24 [90/156160] via 10.21.21.2, 17:42:12, FastEthernet0/1
D 10.10.8.0/24 [90/156160] via 10.21.21.2, 17:42:12, FastEthernet0/1
D 10.10.9.0/24 [90/156160] via 10.21.21.2, 17:42:12, FastEthernet0/1
D 10.3.3.0/30 [90/30720] via 10.21.21.2, 17:42:12, FastEthernet0/1
D 10.10.10.0/24 [90/156160] via 10.21.21.2, 17:42:12, FastEthernet0/1
C 10.21.21.0/30 is directly connected, FastEthernet0/1
C 10.2.2.0/30 is directly connected, FastEthernet0/0
C 10.100.100.1/32 is directly connected, Loopback100
rtr1>
rtr1>sh ip bgp
BGP table version is 45, local router ID is 10.100.100.1
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
*> 10.2.2.0/30 0.0.0.0 0 32768 ?
*> 10.3.3.0/30 10.21.21.2 30720 32768 ?
*> 10.10.1.0/24 0.0.0.0 0 32768 ?
*> 10.10.2.0/24 0.0.0.0 0 32768 ?
*> 10.10.3.0/24 0.0.0.0 0 32768 ?
*> 10.10.4.0/24 0.0.0.0 0 32768 ?
*> 10.10.5.0/24 0.0.0.0 0 32768 ?
*> 10.10.6.0/24 10.21.21.2 156160 32768 ?
*> 10.10.7.0/24 10.21.21.2 156160 32768 ?
*> 10.10.8.0/24 10.21.21.2 156160 32768 ?
*> 10.10.9.0/24 10.21.21.2 156160 32768 ?
*> 10.10.10.0/24 10.21.21.2 156160 32768 ?
*> 10.21.21.0/30 0.0.0.0 0 32768 ?
*> 10.100.100.1/32 0.0.0.0 0 32768 ?
rtr1>
!
router bgp 100
no synchronization
neighbor 10.2.2.2 remote-as 200
neighbor 11.2.2.2 remote-as 100
neighbor 11.2.2.2 next-hop-self
no auto-summary
!
MSFC1#sh ip route
C 127.0.0.0/8 is directly connected, EOBC0
10.0.0.0/8 is variably subnetted, 14 subnets, 3 masks
B 10.10.1.0/24 [20/0] via 10.2.2.2, 00:21:22
B 10.10.2.0/24 [20/0] via 10.2.2.2, 00:21:22
B 10.10.3.0/24 [20/0] via 10.2.2.2, 00:21:22
B 10.10.4.0/24 [20/0] via 10.2.2.2, 00:21:22
B 10.10.5.0/24 [20/0] via 10.2.2.2, 00:21:22
B 10.10.6.0/24 [20/156160] via 10.2.2.2, 00:21:22
B 10.10.7.0/24 [20/156160] via 10.2.2.2, 00:21:22
B 10.10.8.0/24 [20/156160] via 10.2.2.2, 00:21:22
B 10.10.9.0/24 [20/156160] via 10.2.2.2, 00:21:22
B 10.21.21.0/30 [20/0] via 10.2.2.2, 00:21:22
B 10.10.10.0/24 [20/156160] via 10.2.2.2, 00:21:22
C 10.3.3.0/30 is directly connected, Vlan3
C 10.2.2.0/30 is directly connected, Vlan2
B 10.100.100.1/32 [20/0] via 10.2.2.2, 00:21:23
11.0.0.0/30 is subnetted, 2 subnets
C 11.3.3.0 is directly connected, Vlan5
C 11.2.2.0 is directly connected, Vlan4
MSFC1#
MSFC1#sh ip bgp
BGP table version is 15, local router ID is 11.3.3.1
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
*> 10.2.2.0/30 10.2.2.2 0 0 200 ?
*> 10.3.3.0/30 10.2.2.2 30720 0 200 ?
*> 10.10.1.0/24 10.2.2.2 0 0 200 ?
*> 10.10.2.0/24 10.2.2.2 0 0 200 ?
*> 10.10.3.0/24 10.2.2.2 0 0 200 ?
*> 10.10.4.0/24 10.2.2.2 0 0 200 ?
*> 10.10.5.0/24 10.2.2.2 0 0 200 ?
*> 10.10.6.0/24 10.2.2.2 156160 0 200 ?
*> 10.10.7.0/24 10.2.2.2 156160 0 200 ?
*> 10.10.8.0/24 10.2.2.2 156160 0 200 ?
*> 10.10.9.0/24 10.2.2.2 156160 0 200 ?
*> 10.10.10.0/24 10.2.2.2 156160 0 200 ?
*> 10.21.21.0/30 10.2.2.2 0 0 200 ?
*> 10.100.100.1/32 10.2.2.2 0 0 200 ?
MSFC1#
!
router bgp 100
no synchronization
bgp log-neighbor-changes
neighbor 11.2.2.1 remote-as 100
neighbor 11.22.22.2 remote-as 400
no auto-summary
!
rtr3>sh ip route
10.0.0.0/8 is variably subnetted, 14 subnets, 3 masks
B 10.10.1.0/24 [200/0] via 11.2.2.1, 00:05:40
B 10.10.2.0/24 [200/0] via 11.2.2.1, 00:05:40
B 10.10.3.0/24 [200/0] via 11.2.2.1, 00:05:40
B 10.10.4.0/24 [200/0] via 11.2.2.1, 00:05:40
B 10.10.5.0/24 [200/0] via 11.2.2.1, 00:05:40
B 10.10.6.0/24 [200/156160] via 11.2.2.1, 00:05:40
B 10.10.7.0/24 [200/156160] via 11.2.2.1, 00:05:40
B 10.10.8.0/24 [200/156160] via 11.2.2.1, 00:05:40
B 10.10.9.0/24 [200/156160] via 11.2.2.1, 00:05:40
B 10.21.21.0/30 [200/0] via 11.2.2.1, 00:05:40
B 10.10.10.0/24 [200/156160] via 11.2.2.1, 00:05:40
B 10.2.2.0/30 [200/0] via 11.2.2.1, 00:05:40
B 10.3.3.0/30 [200/30720] via 11.2.2.1, 00:05:41
B 10.100.100.1/32 [200/0] via 11.2.2.1, 00:05:41
11.0.0.0/8 is variably subnetted, 7 subnets, 2 masks
C 11.11.1.0/24 is directly connected, Loopback1
C 11.11.2.0/24 is directly connected, Loopback2
C 11.11.3.0/24 is directly connected, Loopback3
C 11.11.4.0/24 is directly connected, Loopback4
C 11.11.5.0/24 is directly connected, Loopback5
C 11.22.22.0/24 is directly connected, Ethernet0/1
C 11.2.2.0/30 is directly connected, Ethernet0/0
12.0.0.0/24 is subnetted, 1 subnets
C 12.12.1.0 is directly connected, Loopback6
rtr3>
rtr3> sh ip bgp
BGP table version is 15, local router ID is 12.12.1.1
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
*>i10.2.2.0/30 11.2.2.1 0 100 0 200 ?
*>i10.3.3.0/30 11.2.2.1 30720 100 0 200 ?
*>i10.10.1.0/24 11.2.2.1 0 100 0 200 ?
*>i10.10.2.0/24 11.2.2.1 0 100 0 200 ?
*>i10.10.3.0/24 11.2.2.1 0 100 0 200 ?
*>i10.10.4.0/24 11.2.2.1 0 100 0 200 ?
*>i10.10.5.0/24 11.2.2.1 0 100 0 200 ?
*>i10.10.6.0/24 11.2.2.1 156160 100 0 200 ?
*>i10.10.7.0/24 11.2.2.1 156160 100 0 200 ?
*>i10.10.8.0/24 11.2.2.1 156160 100 0 200 ?
*>i10.10.9.0/24 11.2.2.1 156160 100 0 200 ?
*>i10.10.10.0/24 11.2.2.1 156160 100 0 200 ?
*>i10.21.21.0/30 11.2.2.1 0 100 0 200 ?
*>i10.100.100.1/32 11.2.2.1 0 100 0 200 ?
rtr3>
!
router bgp 400
bgp log-neighbor-changes
network 11.0.0.0
neighbor 11.22.22.1 remote-as 100
no auto-summary
!
04-07-2003 01:06 AM
AND RTR 4
rtr4#sh ip route
10.0.0.0/8 is variably subnetted, 15 subnets, 3 masks
B 10.10.1.0/24 [20/0] via 11.22.22.1, 00:06:42
B 10.10.2.0/24 [20/0] via 11.22.22.1, 00:06:42
B 10.10.3.0/24 [20/0] via 11.22.22.1, 00:06:42
B 10.10.4.0/24 [20/0] via 11.22.22.1, 00:06:42
B 10.10.5.0/24 [20/0] via 11.22.22.1, 00:06:42
B 10.10.6.0/24 [20/0] via 11.22.22.1, 00:06:42
B 10.10.7.0/24 [20/0] via 11.22.22.1, 00:06:42
B 10.10.8.0/24 [20/0] via 11.22.22.1, 00:06:42
B 10.10.9.0/24 [20/0] via 11.22.22.1, 00:06:42
B 10.21.21.0/30 [20/0] via 11.22.22.1, 00:06:42
B 10.10.10.0/24 [20/0] via 11.22.22.1, 00:06:42
B 10.2.2.0/30 [20/0] via 11.22.22.1, 00:06:42
B 10.3.3.0/30 [20/0] via 11.22.22.1, 00:06:44
C 10.201.201.0/24 is directly connected, Ethernet1/0
B 10.100.100.1/32 [20/0] via 11.22.22.1, 00:06:44
11.0.0.0/8 is variably subnetted, 7 subnets, 2 masks
C 11.11.6.0/24 is directly connected, Loopback1
C 11.11.7.0/24 is directly connected, Loopback2
C 11.11.8.0/24 is directly connected, Loopback3
C 11.11.9.0/24 is directly connected, Loopback4
C 11.11.10.0/24 is directly connected, Loopback5
C 11.22.22.0/24 is directly connected, FastEthernet0/1
C 11.3.3.0/30 is directly connected, FastEthernet0/0
rtr4#
rtr4#sh ip bgp
BGP table version is 143, local router ID is 11.11.10.1
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
*> 10.2.2.0/30 11.22.22.1 0 100 200 ?
*> 10.3.3.0/30 11.22.22.1 0 100 200 ?
*> 10.10.1.0/24 11.22.22.1 0 100 200 ?
*> 10.10.2.0/24 11.22.22.1 0 100 200 ?
*> 10.10.3.0/24 11.22.22.1 0 100 200 ?
*> 10.10.4.0/24 11.22.22.1 0 100 200 ?
*> 10.10.5.0/24 11.22.22.1 0 100 200 ?
*> 10.10.6.0/24 11.22.22.1 0 100 200 ?
*> 10.10.7.0/24 11.22.22.1 0 100 200 ?
*> 10.10.8.0/24 11.22.22.1 0 100 200 ?
*> 10.10.9.0/24 11.22.22.1 0 100 200 ?
*> 10.10.10.0/24 11.22.22.1 0 100 200 ?
*> 10.21.21.0/30 11.22.22.1 0 100 200 ?
*> 10.100.100.1/32 11.22.22.1 0 100 200 ?
rtr4#
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