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basic question bgp/static

hi guys,. a very basic question, i just need some insight in to what is happening here. 10.128.192.1/18 is known to R2 via a static route and bgp is advertising this network on R2. my problem is with the last picture. why is R3 not showing it as a route when i do show ip route 10.128.192.0. it only shows the /24 by default unless i specify /18 although it is learning both as can be seen.

 

 

11.PNG12.PNG13.PNG14.PNG15.PNG16.PNG

1 ACCEPTED SOLUTION

Accepted Solutions

Hi @ahmedsid432135621 ,

 

This is normal behavior in IOS. When you do a

"show ip route <prefix>" 

it will show you only the most specific prefix, as you do not specify a prefix length. If you want to see all prefixes, you need to do

"show ip route 10.128.192.0 255.255.192.0 longer-prefixes" or "show ip route 10.128.0.0 255.255.0.0 longer-prefixes",

as suggested by @Georg Pauwen . This command will show all the received prefixes matching the "prefix/prefix length" specified and the more specific prefixes.

 

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

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7 REPLIES 7
Georg Pauwen
VIP Master

Hello,

 

not really sure what you are asking. Are you trying to display all routes that match the specified prefix ?

 

Try:

 

show ip route 10.128.192/0 255.255.192.0 longer-prefixes

 

MHM Cisco World
Advisor

both is easy since there is Lo in R2 and you config redistribute connected, so it advertise the Lo and static route. 
why /18 because the BGP not advertise prefix if it not same as appear in routing table.

what i mean is, i cant understand the logic behind the display. why doesnt it display both networks, is it because of the longest prefix match? the 18 network is advertised by R2 specifically configured.

But i see both in one photo you share.

One is lo and other of static route.

Lo with /24

Static route /18

Hello,

 

do you have the full configs of all three routers so we can lab this up ?

Hi @ahmedsid432135621 ,

 

This is normal behavior in IOS. When you do a

"show ip route <prefix>" 

it will show you only the most specific prefix, as you do not specify a prefix length. If you want to see all prefixes, you need to do

"show ip route 10.128.192.0 255.255.192.0 longer-prefixes" or "show ip route 10.128.0.0 255.255.0.0 longer-prefixes",

as suggested by @Georg Pauwen . This command will show all the received prefixes matching the "prefix/prefix length" specified and the more specific prefixes.

 

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
MHM Cisco World
Advisor

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