North American Network Operators Group

Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical

RE: BGP Redistribution question

  • From: Michael Dell
  • Date: Thu Aug 05 11:27:16 2004

Hi there

The redistribution information you have set in BGP only redistributes routes
*learnt* via OSPF into BGP.

An alternative solution to using the network command in BGP would have been
to use the "redistribute static" command from within the BGP process
context.  This would be similar to the redistribute static command you had
set up within the OSPF context.

The network command tells BGP to originate a route for that network whether
or not such a route exists in the router's IP route table, which means it
has no connection with the static IP route you defined.

Hope that helps.

Mike Dell
Networking Protocols Group
Data Connection Ltd
Tel: +44 20 8366 1177
Fax: +44 20 8367 8501
E-mail: [email protected]
Web: http://www.dataconnection.com



-----Original Message-----
From: [email protected] [mailto:[email protected]]On Behalf Of D
Train
Sent: 05 August 2004 16:09
To: [email protected]
Subject: BGP Redistribution question



While looking into a routing issue, I found that one
of my routers wasn't passing one of my static routes,
being redist into ospf into bgp, and not sure as to
why. It has been a while since I have worked with BGP,
so I am a little rusty. The solution was for me to add
the following BGP network statement... network
10.86.8.0 mask 255.255.248.0. If statics are being
redist info ospf, and ospf is basically being redist
into bgp, why did I have to have the network
statement. Why didn't it put it into BGP and pass it
along?

Here is the scenario:
Router A:
ip route 10.86.8.0 255.255.248.0 10.86.138.14

ATL--CR6513A#ping 10.86.138.14
success rate is 100 percent (5/5), round-trip
min/avg/max = 1/1/4 ms

ATL -CR6513A#sh ip route 10.86.8.0 
Routing entry for 10.86.8.0/21
Known via "static", distance 1, metric 0
Redistributing via ospf 1
Advertised by ospf 1 subnets
bgp 2
Routing Descriptor Blocks:
* 10.86.138.14
Route metric is 0, traffic share count is 1

ATL-CR6513A#sh ip ospf data ext 10.86.8.0
OSPF Router with ID (10.86.194.5) (Process ID 1)
Type-5 AS External Link States
Routing Bit Set on this LSA
LS age: 898
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 10.86.8.0 (External Network Number )
Advertising Router: 10.86.194.2
LS Seq Number: 80000D87
Checksum: 0x3D49
Length: 36
Network Mask: /21
Metric Type: 2 (Larger than any link state path)
TOS: 0 
Metric: 20 
Forward Address: 0.0.0.0
External Route Tag: 0
LS age: 554
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 10.86.8.0 (External Network Number )
Advertising Router: 10.86.194.5
LS Seq Number: 80000D87
Checksum: 0x2B58
Length: 36
Network Mask: /21
Metric Type: 2 (Larger than any link state path)
TOS: 0 
Metric: 20 
Forward Address: 0.0.0.0
External Route Tag: 0

ATL-CR6513A#sh ip bgp 10.86.8.0
BGP routing table entry for 10.86.0.0/16, version
1078065
Paths: (2 available, best #2, table
Default-IP-Routing-Table)
Multipath: eBGP
Advertised to non peer-group peers:
10.1.2.9 
1, (aggregated by 1 10.1.254.253)
10.1.2.9 from 10.1.2.9 (10.1.254.253)
Origin IGP, metric 0, localpref 100, valid, external,
atomic-aggregate, multipath
1, (aggregated by 1 10.1.254.252)
10.1.2.1 from 10.1.2.1 (10.1.254.252)
Origin IGP, metric 0, localpref 100, valid, external,
atomic-aggregate, multipath, best

router ospf 1
redistribute static subnets
router bgp 2
no synchronization
network x.x.x.x
network y.y.y.y
network 10.86.8.0 mask 255.255.248.0 ***had to be
added for this to work, but wasn't present before
hand***
redistribute connected route-map OSPF-Links
redistribute ospf 1 route-map WW-OSPF-Routes
neighbor 10.1.2.1 remote-as 1
neighbor 10.1.2.1 advertisement-interval 1
neighbor 10.1.2.9 remote-as 1
neighbor 10.1.2.9 advertisement-interval 1
maximum-paths 2
no auto-summary

route-map WW-OSPF-Routes permit 10
set metric-type internal

This is I was seeing on my Upstream Core router:
ATL -CR12406A#sh ip route 10.86.8.0
Routing entry for 10.86.0.0/16
Known via "bgp 1", distance 200, metric 0, type
locally generated
Routing Descriptor Blocks:
* directly connected, via Null0
Route metric is 0, traffic share count is 1
AS Hops 0, BGP network version 
 
This is what I was seeing after I add the network
statement:

GAATL-WW1-CR12406A#sh ip bgp 10.86.8.0

BGP routing table entry for 10.86.8.0/21, version
2210556

Paths: (2 available, best #2, Advertisements
suppressed by an aggregate.)

Multipath: eBGP iBGP
Not advertised to any peer
2
10.1.2.2 from 10.1.2.2 (10.86.194.5)
Origin IGP, metric 0, localpref 100, valid, external,
multipath
2
10.1.2.6 from 10.1.2.6 (10.86.194.2)
Origin IGP, metric 0, localpref 100, valid, external,
multipath, best

 




		
__________________________________
Do you Yahoo!?
Yahoo! Mail Address AutoComplete - You start. We finish.
http://promotions.yahoo.com/new_mail