Connectivity Guide
Advertise cost
As the default process for redistributed routes, OS10 supports IGP cost as MED. Both auto-summarization and synchronization are disabled
by default.
BGPv4 and BGPv6 support
• Deterministic MED, default
• A path with a missing MED is treated as worst path and assigned an 0xffffffff MED value
• Delayed conguration at system boot — OS10 reads the entire conguration le BEFORE sending messages to start BGP peer
sessions
4-Byte AS numbers
OS10 supports 4-byte AS number congurations by default. The 4-byte support is advertised as a new BGP capability - 4-BYTE-AS, in
the OPEN message. A BGP speaker that advertises 4-Byte-AS capability to a peer, and receives the same from that peer must encode AS
numbers as 4-octet entities in all messages.
If the AS number of the peer is dierent, the 4-byte speaker brings up the neighbor session using a reserved 2-byte ASN, 23456 called
AS_TRANS. The AS_TRANS is used to interop between a 2-byte and 4-byte AS number.
Where the 2-byte format is 1 to 65535, the 4-byte format is 1 to 4294967295. You can enter AS numbers using the traditional format.
AS number migration
You can transparently change the AS number of an entire BGP network. Changing the AS number ensures that the routes propagate
throughout the network while migration is in progress. When migrating one AS to another and combining multiple AS, an EBGP network
may lose its routing to an IBGP if the AS number changes.
Migration is dicult as all IBGP and EBGP peers of the migrating network must be updated to maintain network reachability. Local-AS
allows the BGP speaker to operate as if it belongs to a virtual AS network besides its physical AS network.
Disable the local-as command after migration. Failure to disable the local-as command after migration causes the local-as
command to replace the original AS number of the system. You must recongure the system with a new AS number.
436
Layer 3