Label Distribution Protocol
416
MPLS Guide
© 2022 Nokia.
Use subject to Terms available at: www.nokia.com
3HE 18686 AAAB TQZZA
Adjacency capability elements are encoded as follows:
01234567
+-+-+-+-+-+-+-+-+
|D| CapFlag |
+-+-+-+-+-+-+-+-+
D bit: Controls the capability state.
• 1 : Disable capability
• 0 : Enable capability
CapFlag: The adjacency capability
• 1 : Prefix IPv4 forwarding
• 2 : Prefix IPv6 forwarding
• 3 : P2MP IPv4 forwarding
• 4 : P2MP IPv6 forwarding (not supported on the 7705 SAR)
• 5 : MP2MP IPv4 forwarding
• 6 : MP2MP IPv6 forwarding
Each CapFlag appears no more than once in the TLV. If duplicates are found, the
D-bit of the first element is used. For forward compatibility, if the CapFlag is
unknown, the receiver must silently discard the element and continue processing the
rest of the TLV.
5.4.6 IP Address and FEC Distribution
When an LDP LSR initializes the LDP session to the peer LSR and the session
comes up, IP addresses and FECs are distributed. Local IPv4 and IPv6 interface
addresses are exchanged using the Address and Address Withdraw messages.
FECs are exchanged using label mapping messages.
By default, IPv6 address distribution is determined by whether the dual-stack
capability TLV, which is defined in draft-ietf-mpls-ldp-ipv6, is present in the Hello
message from the peer. This requirement is designed to address interoperability
issues found with existing third-party LDP IPv4 implementations.
IP address and FEC distribution behavior is described below.
• If the peer LSR sent the dual-stack capability TLV in the Hello message, then
local IPv6 addresses are sent to the peer. The user can configure an address
export policy to restrict which local IPv6 interface addresses are sent to the peer.
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