Solved: BGP best path selection

shibindong · ‎06-24-2008

sorry to ask you a basic question:

according to BGP bast path selection:

1. weight

2. local preference

3. original type: locally originated"network" command or "redistribut" command > "aggregate-addrfess"

4. AS-PATH

5. IGP<EGP<incomplete

My question here is if the route been redistributed, does it match origianl type (step 3) or match imcomplete?

and what is the difference between 3 and 5?

Edison Ortiz · ‎06-24-2008

The first output looks odd to me if issued on the router where you perform the redistribute static.

You should have 0.0.0.0 instead of 172.16.0.1 IP address.

0.0.0.0 indicates the route is locally generated.

I quickly pull up my lab and duplicated your scenario.

Rack1R2(config)#ip route 3.3.3.3 255.255.255.255 null0

Rack1R2(config)#router bgp 1

Rack1R2(config-router)#redistribute static

!

Rack1R2#sh ip bgp 3.3.3.3

BGP routing table entry for 3.3.3.3/32, version 5

Paths: (1 available, best #1, table Default-IP-Routing-Table)

Flag: 0x820

Advertised to update-groups:

1

Local

0.0.0.0 from 0.0.0.0 (150.1.2.2)

Origin incomplete, metric 0, localpref 100, weight 32768, valid, sourced, best

!

As for your 2nd query. The "i" stands for internal route. If you type show ip bgp, you will see a legend with information of what each character means.

Here is a sample legend

Rack1R2#sh ip bgp

BGP table version is 5, local router ID is 150.1.2.2

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

HTH,

__

Edison.

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View solution in original post

Edison Ortiz · ‎06-24-2008

Step 3 is for locally originated routes, in other words, the router in question brought those routes into BGP.

Step 5 is for routes learned from other BGP speaking routers.

As for your question, it can match step 3 or 'incomplete', it all depends who originated the route as I explained above.

HTH,

__

Edison.

Please rate helpful posts

shibindong · ‎06-24-2008

thanks for your reply, one more question: I add a static route in the router: ip route 3.3.3.3 255.255.255.255 null0" and "redistribute static" under BGP process, can I say I originate the route locally? But I saw the output is this:

"POP#sh ip bgp 3.3.3.3

BGP routing table entry for 3.3.3.3/32, version 14

Paths: (1 available, best #1, table Default-IP-Routing-Table)

Advertised to non peer-group peers:

192.168.21.99

Local

172.16.0.1 (metric 193) from 172.16.0.1 (172.16.0.1)

Origin incomplete, metric 0, localpref 100, valid, internal, best"

it show me "incomplete", and by the way, what is the first "i" stand for in the output"

*>i192.22.12.0/30 192.168.20.22 0 100 0 22 i"?

a.alekseev · ‎06-24-2008

the first "i" means internal

http://www.cisco.com/en/US/docs/internetworking/case/studies/icsbgp4.html#wp3760

Edison Ortiz · ‎06-24-2008

The first output looks odd to me if issued on the router where you perform the redistribute static.

You should have 0.0.0.0 instead of 172.16.0.1 IP address.

0.0.0.0 indicates the route is locally generated.

I quickly pull up my lab and duplicated your scenario.

Rack1R2(config)#ip route 3.3.3.3 255.255.255.255 null0

Rack1R2(config)#router bgp 1

Rack1R2(config-router)#redistribute static

!

Rack1R2#sh ip bgp 3.3.3.3

BGP routing table entry for 3.3.3.3/32, version 5

Paths: (1 available, best #1, table Default-IP-Routing-Table)

Flag: 0x820

Advertised to update-groups:

1

Local

0.0.0.0 from 0.0.0.0 (150.1.2.2)

Origin incomplete, metric 0, localpref 100, weight 32768, valid, sourced, best

!

As for your 2nd query. The "i" stands for internal route. If you type show ip bgp, you will see a legend with information of what each character means.

Here is a sample legend

Rack1R2#sh ip bgp

BGP table version is 5, local router ID is 150.1.2.2

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

HTH,

__

Edison.

Please rate helpful posts

wilson_1234_2 · ‎11-05-2009

Edison,

This is an old post, but I am curious about something.

When you said "I quickly pull up my lab and duplicated your scenario."

How was this done?

Is your lab actual hardware, or do you have a simulated lab environment?

Edison Ortiz · ‎11-05-2009

Hi Richard,

I actually have both - actual hardware and GNS3.

This was a while ago so I don't remember which I used - but I think it was actual hardware.

Regards

Edison.