Users Guide

• deterministic multi-exit discriminator (MED) (default)
• a path with a missing MED is treated as worst path and assigned an MED value of (0x)
• the community format follows RFC 1998
• delayed conguration (the software at system boot reads the entire conguration le prior to sending messages to start BGP peer
sessions)
The following are not yet supported:
• auto-summarization (the default is no auto-summary)
• synchronization (the default is no synchronization)
Conguring a basic BGP network
Conguring a basic BGP network includes a few mandatory tasks and many optional tasks. The initial step is to congure a BGP routing
and BGP peers, using the address family conguration. You can also congure BGP peers using the IPv4 VRF address family.
Enabling BGP
By default, BGP is disabled on the system. Dell EMC Networking OS supports one autonomous system (AS) and assigns the AS number
(ASN). To enable the BGP process and begin exchanging information, assign an AS number and use commands in ROUTER BGP mode to
congure a BGP neighbor.
To establish BGP sessions and route trac, congure at least one BGP neighbor or peer.
In BGP, routers with an established TCP connection are called neighbors or peers. After a connection is established, the neighbors
exchange full BGP routing tables with incremental updates afterward. In addition, neighbors exchange KEEPALIVE messages to maintain
the connection.
In BGP, neighbor routers or peers can be classied as internal or external. External BGP peers must be connected physically to one another
(unless you enable the EBGP multihop feature), while internal BGP peers do not need to be directly connected. The IP address of an EBGP
neighbor is usually the IP address of the interface directly connected to the router. First, the BGP process determines if all internal BGP
peers are reachable, then it determines which peers outside the AS are reachable.
Following is the sample conguration steps to enable BGP, congure a BGP router-id and network for a router. The same congurations
have to be repeated with appropriate changes in the IP addresses for a peer or router to achieve BGP session between two devices. In the
below conguration example, no address family is congured. So, the routing information for the IPv4 unicast address family is advertised
by default.
1 Assign an AS number and enter ROUTER BGP mode.
CONFIGURATION mode
router bgp as-number
• as-number: from 0 to 65535 (2 Byte) or from 1 to 4294967295 (4 Byte) or 0.1 to 65535.65535 (Dotted format).
Only one AS is supported per system.
NOTE
: If you enter a 4-Byte AS number, 4-Byte AS support is enabled automatically.
2 Enable 4-Byte support for the BGP process.
CONFIG-ROUTER-BGP mode
bgp four-octet-as-support
NOTE
: This command is OPTIONAL. Use it only if you support 4-Byte AS numbers or if you support AS4 number
representation. Disable 4-Byte support and return to the default 2-Byte format by using the no bgp four-octet-as-
support command. You cannot disable 4-Byte support if you currently have a 4-Byte ASN congured.
Border Gateway Protocol (BGP) 199