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Help with some BGP configuration.

network_geek1979
Beginner
Beginner

I need some help configuring BGP on our new router. This time we are using a 6-byte BGP AS number and our service provider has a 4-byte BGP. We are having a Cisco 4431 series router which should support this. Is there anything different in the configuration part?

 

regards,

N.

7 Replies 7

shaps
Participant
Participant

I wasn't even aware that there was 6 byte AS numbers,  can you show me some documentation on this ?

Hello

I think there is a confusion here with "6-digit AS number"? As far as I know there's no 6-byte BGP ASN. Of course the new format with 4-byte BGP ASN is supported on your platform on the IOS XE since version 3.13.0S.

I recommend you use the Cisco Feature Navigator when researching available features: http://tools.cisco.com/ITDIT/CFN/jsp/index.jsp

Best regards,
Martin

I apologize for my confusion between 4-byte and 6-byte.

 

We have a 4-byte AS and the service provider will have a 2-byte AS.

there shouldn't be problem,   I  believe the routers take care of the difference with little input needed.  

I apologize for my confusion between 4-byte and 6-byte.

 

We have a 4-byte AS and the service provider will have a 2-byte AS.

mdella000
Beginner
Beginner

There currently is no such thing as a 6-byte AS number.  Prior to 2007, AS numbers were 2-byte (or 16 bit) numbers ranging from 0-65535 where some of those were reserved for private use (ie, not to be used on the actual internet).  Just like IP addresses however, there was a push to expand the number of AS numbers available as the usage continued to go up.  So another RFC was published to push AS numbers from 16 bits to 32 bits (2-byte to 4-byte).  Since around 2010, IANA has been issuing 32bit AS numbers rather than the older 16bit numbers.

Representation of these numbers look as follows:

For original 16bit AS number (like my personal one)

AS-Plain: 4432

AS-Dot: 0.4432

For newer 32bit AS numbers, you might see something like:

AS-Plain: 65560

AS-Dot: 1.24  (where you computed 1 * 65536 + 24 = 65560)

...

To use your router in "AS-Dot" notation, you need to use the command "bgp annotation dot" then you can use the dot notation in your BGP commands.  Be aware that cisco uses "10.1" as an example ASN however they often miswrite what the AS-Plain version of that is (its really a bad example).

AS-Dot: 10.1 = 10 * 65536 + 1 = 655361 (which when written can be confusing if miswritten)

---

quick example: if your ASN (AS-Plain) was 66123, then your AS-Dot would be (1 * 65536 + 587) or 1.587

bgp router 1.587

  no synchronization

  bgp router id 64.22.52.1

  bgp annotation dot

  bgp log-neighbor-changes

  ...etc...

 

 

Marcos (BGP Engineer since 1992)

I apologize for my confusion between 4-byte and 6-byte.

 

We have a 4-byte AS and the service provider will have a 2-byte AS.

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