07-02-2009 01:01 AM - edited 03-04-2019 05:17 AM
Hi all ,
I am having problem on understanding BGP deterministic MED . When issue the command of sh ip bgp . I can see my internal routes were assigned the value of 150 under Metric .
But when , i search in the confguration , i can't see any configuration , to specify the metric 150 . I have only specify my OSPF cost of 50000 . On my WAN Router i have specified BGP deterministic med . My router directly connected to ISP Router which connects to another site .
07-02-2009 11:20 AM
Hello Alman,
post the output of
sh ip bgp
and relevant configuration
BGP deterministic MED should be involved just in path selection not on the seed metric value.
Are you redistributing OSPF into BGP?
Be also aware that MED could have been reassigned on the other side device with a route-map.
see command reference at
http://www.cisco.com/en/US/partner/docs/ios/iproute/command/reference/irp_bgp1.html#wp1012961
Hope to help
Giuseppe
07-05-2009 04:02 AM
Thanks Giuseppe,
I am sorry , I am still new to BGP . You mean
sh ip bgp
I am redistributing BGP in OSPF .
On the otherside , i have checked the route map is to receive the routes from this particular site and is in different AS . I believe the MED value will not be carried outside the AS .
I have the same configuration on my both WAN Routers . I can see the same things , the internal routes with seed metric of 150 . I believe this has been done to influance the incoming traffic to take both sides , load balancing , I believe.
I am not able to see the url that you sent . It says , special requirement needed .
Thanks
07-05-2009 11:18 AM
Hello,
>> I believe the MED value will not be carried outside the AS
MED = multi exit discriminator is passed to neighboring AS in an eBGP session no special configuration is required.
It is the local preference attribute that is not passed to a neighboring AS.
I wonder if you are calling MED the local preference.
see this link
http://www.cisco.com/en/US/docs/internetworking/technology/handbook/bgp.html#wp1020591
I will give you a link that you can open:
Edit:
link to command reference deterministic med
http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_bgp1.html#wp1012961
When I say sh ip bgp
I mean the prefix you say that BGP deterministic med has caused a change in BGP metric attribute.
if you like you can post the
sh ip bgp
this command is very useful because it shows all known BGP paths to the destination with all their BGP attributes in a format that is easy to be read.
Hope to help
Giuseppe
07-06-2009 04:33 AM
Thanks Giuseppe,
I will post the configurations . Two of my WAN Routers are facing the ISP and connected to other site . But I dont have the access to ISP Routers . I can't give the ISP router's output .
Regards
07-06-2009 12:26 PM
Hello Alman,
let's see your current configurations.
I understand this is a production network and not a lab setup.
Hope to help
Giuseppe
07-06-2009 05:07 PM
Hi Giuseppe,
Below is the config
interface Loopback0
ip address 2.2.2.2 255.255.255.255
no ip redirects
no ip unreachables
no ip proxy-arp
!
interface Null0
no ip unreachables
!
interface GigabitEthernet0/0
ip address 3.3.3.3 255.255.255.252
no ip redirects
no ip proxy-arp
ip route-cache flow
ip ospf network point-to-point
ip ospf dead-interval minimal hello-multiplier 4
duplex auto
speed auto
media-type sfp
!
interface GigabitEthernet0/1
ip address 4.4.4.4 255.255.255.252
no ip redirects
no ip proxy-arp
ip route-cache flow
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 7 062F0E15586F582B1135
ip ospf network point-to-point
ip ospf dead-interval minimal hello-multiplier 4
duplex auto
speed auto
media-type rj45
!
interface FastEthernet1/0
ip address 5.5.5.5 255.255.255.252
no ip redirects
no ip proxy-arp
ip route-cache flow
duplex full
speed 100
max-reserved-bandwidth 100
!
interface FastEthernet1/1
no ip address
shutdown
duplex auto
speed auto
!
router ospf 1
router-id 2.2.2.2
log-adjacency-changes
auto-cost reference-bandwidth 50000
area 0 authentication message-digest
redistribute bgp 10 metric-type 1 subnets
passive-interface default
no passive-interface GigabitEthernet0/0
no passive-interface GigabitEthernet0/1
network 2.2.2.2 0.0.0.0 area 0
network 3.3.3.3 0.0.0.0 area 0
network 4.4.4.4 0.0.0.0 area 0
default-information originate
!
router bgp 10
bgp log-neighbor-changes
bgp deterministic-med
neighbor ISP peer-group
neighbor ISP remote-as 100
neighbor INTERNAL peer-group
neighbor INTERNAL remote-as 10
neighbor INTERNAL password 7 1526052D551E39003107
neighbor INTERNAL update-source Loopback0
neighbor INTERNAL timers 2 6
neighbor 2.2.2.1 peer-group INTERNAL
neighbor 20.20.20.20 peer-group ISP
!
address-family ipv4
neighbor ISP send-community both
neighbor ISP soft-reconfiguration inbound
neighbor ISP route-map ROUTES_IN in
neighbor ISP route-map ROUTES_OUT out
neighbor ISP filter-list 66 out
neighbor INTERNAL send-community both
neighbor INTERNAL next-hop-self
neighbor INTERNAL soft-reconfiguration inbound
neighbor 2.2.2.1 activate
neighbor 20.20.20.21 activate
no auto-summary
no synchronization
network 3.3.3.0 mask 255.255.255.0
network 4.4.4.0 mask 255.255.255.128
aggregate-address 3.3.0.0 255.255.240.0 summary-only
aggregate-address 4.4.0.0 255.255.240.0 summary-only
exit-address-family
!
no ip http server
no ip http secure-server
ip tacacs source-interface Loopback0
!
!
ip prefix-list 10 seq 5 permit 0.0.0.0/0
ip prefix-list 10 seq 10 permit 6.6.0.0
ip prefix-list 10 seq 15 permit 7.7.0.0
ip prefix-list 10 seq 20 permit 8.8.0.0
ip prefix-list 10 seq 25 permit 9.9.0.0
!
ip prefix-list 20 seq 5 permit 3.3.0.0
ip prefix-list 20 seq 10 permit 4.4.0.0
!
route-map ROUTES_OUT permit 10
match ip address prefix-list 20
!
route-map ROUTES_IN permit 10
match ip address prefix-list 10
!
!
If issue the command of :
sh ip bgp 2.2.2.0
BGP routing table entry for 2.2.2.0/24, version 49
Paths: (1 available, best #1, table Default-IP-Routing-Table, Advertisements suppressed by an aggregate.)
Not advertised to any peer
Local
2.2.2.20 from 0.0.0.0 (2.2.2.2)
Origin IGP, metric 150, localpref 100, weight 32768, valid, sourced, local, best
07-07-2009 12:03 AM
Hello Alman,
Local
2.2.2.20 from 0.0.0.0 (2.2.2.2)
Origin IGP, metric 150, localpref 100, weight 32768, valid, sourced, local, best
the route is generated locally by the router with origin IGP weight 32768 next-hop 0.0.0.0.
The MED field is copied from IGP metric you can check this with
sh ip ospf int loop0
if the OSPF cost you see here is 150 you are fine.
Notice that you have changed the auto-reference BW in OSPF.
auto-cost reference-bandwidth 50000
Hope to help
Giuseppe
07-07-2009 05:58 AM
Hi ,
Yes , you are correct,it comes from the OSPF cost . I have changed the default cost .So , does it mean the MED is 150 ,and being advertised to other routers . Both WAN Routers has the same output , does it mean , it's being loadbalanced .Is the BGP deterministic , really works in my scenario.
Thanks for your help
07-07-2009 05:38 PM
The cost is actually is 1 .
sorry there's some mistake on the ip address of the loopback that i posted , actually is
2.2.2.1
Below is output of the command .
sh ip ospf int loop0
Loopback0 is up, line protocol is up
Internet Address 2.2.2.1/32, Area 0
Process ID 1, Router ID 2.2.2.1, Network Type LOOPBACK, Cost: 1
Loopback interface is treated as a stub Host
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