Users Guide

Advertise cost
As the default process for redistributed routes, OS10 supports IGP cost as MED. Both autosummarization 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 configuration at system boot—OS10 reads the entire configuration file BEFORE sending messages to start BGP
peer sessions.
4-Byte AS numbers
OS10 supports 4-byte AS number configurations 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 different, 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 also enter AS numbers using the dotted
decimal format. For example, you can enter 0.123.
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 difficult 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. Reconfigure the system with a new AS number.
Router A, Router B, and Router C belong to AS 100, 200, and 300, respectively. Router A acquired Router B — Router B
has Router C as its client. When Router B is migrating to Router A, it must maintain the connection with Router C without
immediately updating Router C’s configuration. Local-AS allows Router B to appear as if it still belongs to Router B’s old
network, AS 200, to communicate with Router C.
Layer 3
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