What is recognized BGP?

[Leftz]

Folks, 

There are two categories of path attributes - Well-known and Optional.

With well known attributes, they must be recognized by all BGP implementations. Well Known attributes comprise of Mandatory and Discretionary attributes.

Anyone can explain recognized? thanks

[MHM Cisco World]

the BGP is list in many RFC.
 and there are many vendor, so each vendor to support BGP must recognized the well-known attribute and other attribute is optional that why you see un-compatible between Router Vendor in some BGP attribute (non well-known).
for example weight attribute is use by only cisco not other vendor. 
https://networklessons.com/bgp/how-to-configure-bgp-weight-attribute

[interfacedy]

@MHM Cisco World Thank you, Agree

[Spooster IT Services]

Hi Zshowip ,

All the Vendors have to Comply to the BGP RFC set by the IETF , Therefore the attributes that are specified in the RFC's are known as the WELL KNOWN attributes as they have to be available irrespective of the  Vendor , but then there is " WEIGHTS " , which is  a vendor specific Attributes used only by cisco .

Note :  A Request for Comments (RFC) is a formal document from the Internet Engineering Task Force (IETF) that contains specifications and organizational notes about topics related to the internet and computer networking, such as routing, addressing and transport technologies.

[Leftz]

Thanks. The reason why there is "recognized" with bgp attribute is because of "weight"  If no "weight", there would not be "recognized", right? 

[MHM Cisco World]

nope, the weight is one of BGP attribute. 
but it not recognized attribute.

[David Ruess · Accepted solution]

Hello,

Recognized just means that every vendors devices (CISCO, JUNIPER, BROCADE, etc) that run BGP have to understand what this attribute does and how its implemented.

• Well-known mandatory: Must be recognized by all BGP routers, present in all BGP updates, and passed on to other BGP routers. For example, AS path, origin, and next hop.
• Well-known discretionary: Must be recognized by all BGP routers and passed on to other BGP routers but need not be present in an update, for example, local preference.

This video may help. First 20-30 minutes should answer your question.

https://www.youtube.com/watch?v=Ly6wg4PdunM

-David

[Leftz]

@MHM Cisco World What's other attribute like Weight? 

"nope, the weight is one of BGP attribute. 
but it not recognized attribute.     "

Here is one of cisco statement:

1. Well-known mandatory:Recognized by all BGP peers, passed to all peers, and present in all Update messages.  Well-known mandatory attributes include:- Next-hop- Origin- AS PATH

I think "well-known" and "recognized" are the same meaning. For example, when cisco router and Juniper router are connected together, the juniper router does not know Weight coming from the cisco router, so we can say the juniper router cannot recognize the Weight, it can recognize all attribute like local-preference coming from the cisco router. So what attribute else juniper router cannot recognize?

Maybe juniper router does not have some small(weak) bgp attribute as Cisco router has. so juniper would not know(recognize) it. Is this meaning of recognized? 

[Giuseppe Larosa · Accepted solution]

Hello @Leftz ,

Cisco weight is not exactly a BGP attribute it is local to the router where you configure it .  So weight is never sent to any BGP peer even if it is another Cisco router. So I would leave weight out of this discussion.

I think that @David Ruess 's answer is the most complete.

Recognized means that the peer's BGP implementation has to understand the BGP attribute type and to be able to pass it to other peers.

Attributes are coded in Type Length Value data structures here the question is just what type values need to be accepted / implemented by all BGP implementations.

Hope to help

Giuseppe

[MHM Cisco World]

""Cisco weight is not exactly a BGP attribute""
I totally Know that weight not send to other but it as cisco mention below is BGP attribute 
"""This document describes the importance of Border Gateway Protocol (BGP) Weight path attribute in network failover scenarios. BGP is commonly used to advertise the network prefixes to the Wan Area Network (WAN) once received via an Interior Gateway protocol (IGP) from the Lan Area Network (LAN) and viceversa. Without the correct configuration in place, BGP can fail to restore the original routing path over the WAN after the network recovers from a link failure."""

https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/213285-understand-the-importance-of-bgp-weight.html

Now the attribute is not easy part of BGP, when I do lab and capture the BGP update and read all attribute exchange between Peer. 
@Leftz  you must clear notice that not only well-known must recognize but also Optional, like community which is transitive attribute if cisco connect to other vendor and cisco send community then other vendor must recognize it.

[MHM Cisco World]

Still checking other attribute for other vender that not recognized, I will update you. 

[Leftz]

Thanks all.