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#VPN MONITOR IN SRX UPDATE#

The Route Target community is used in MPLS VPN environments to separate two customers routing tables, as shown in the following diagram:

This separation is possible due to multiprotocol BGP extensions and MPLS. Basically, you can connect multiple sites of a customer and have a separate routing table (VRF) across the entire network just for this customer and implement routing policies that are different from the routing policies of another customer.

Route Origin community: Identifies the routers that inject a specific set of routes into BGP.Ī Virtual Routing and Forwarding (VRF) is a virtual routing table that can have its own separate routing policies separate from the global routing table or from other VRFs.

Route Target community: Identifies the routers that can receive a specific set of routes.

The most well-known application for extended communities is in MPLS-VPN which makes use of two extended communities: Based on the value of the high-order byte in the Type field, the administrator field can be an AS or an IP address.

Last 6 bytes: Provides unique information specific to the community typeĪn extended community has three fields: type, administrator, assigned number (type:administrator:assigned-number).

First 2 bytes: Specifies community type.

Extended CommunityĪn Extended community is a 8-byte value that is divided into two main sections: Graceful Shutdown BGP Re-Route Example 5.

The following example shows a No-Advertise Route (10.10.10.0/24) not being advertised by R1 to peers R11, R12, R111. When a No-Advertise community is attached to a route, the BGP speaker won’t advertise the route to any internal or external BGP peers. The following are few well-known communities that must be recognized by all community aware BGP implementations. This means that an AS with the ASN 9999 (which in hex is 0x270F) can have communities in the range 0x270F0000 - 0x270FFFFF. Because each AS number is unique, each community is also unique on the internet. The first 16 bits encode the AS number that originated the community and the last 16 bits represent a unique number assigned by the AS. Advanced BGP Community ConceptsĪ community is a 32-bit value split into two 16-bit sections.

#VPN MONITOR IN SRX UPDATE#

Now that you’ve seen what a BGP community looks like within an Update message, let’s begin exploring the more advanced concepts surrounding this attribute. Origin IGP, metric 0, localpref 100, valid, external, best Paths: (1 available, best #1, table default) R111 sets the community 1:110 on the routes it advertises to R11.īGP routing table entry for 10.10.10.0/24, version 2 Consider this simple network, where R111 advertises the 10.10.10.0/24 route to the AS 11 BGP peer. To get started, let’s look at what a BGP community set to a route looks like in an Update message. You might see a BGP community as a tag attached to the BGP routes exchanged between two BGP peers. What Is a BGP Community?Ī BGP community is an optional, transitive BGP attribute that is recognized and passed to other BGP peers. In this article, we’ll explore what kind of BGP communities exist and how you can use them to manipulate network traffic. Although BGP communities represent just one of the BGP attributes available, there’s a lot to be said about them. In that article, we also covered some important definitions that provide context for discussing BGP functionality. In our previous article dedicated to BGP attributes, we covered how routers evaluate BGP attributes found in the Update message to select the best path to be installed in the routing table.