The MPLS router must be configured to synchronize IGP and LDP to minimize packet loss when an IGP adjacency is established prior to LDP peers completing label exchange.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
low	V-256050	SRG-NET-000512-RTR-000003	ARST-RT-000710	SV-256050r882492_rule	2025-02-20	2

Description
Packet loss can occur when an IGP adjacency is established and the router begins forwarding packets using the new adjacency before the LDP label exchange completes between the peers on that link. Packet loss can also occur if an LDP session closes and the router continues to forward traffic using the link associated with the LDP peer rather than an alternate pathway with a fully synchronized LDP session. The MPLS LDP-IGP Synchronization feature provides a means to synchronize LDP with OSPF or IS-IS to minimize MPLS packet loss. When an IGP adjacency is established on a link but LDP-IGP synchronization is not yet achieved or is lost, the IGP will advertise the max-metric on that link.

Description

Packet loss can occur when an IGP adjacency is established and the router begins forwarding packets using the new adjacency before the LDP label exchange completes between the peers on that link. Packet loss can also occur if an LDP session closes and the router continues to forward traffic using the link associated with the LDP peer rather than an alternate pathway with a fully synchronized LDP session. The MPLS LDP-IGP Synchronization feature provides a means to synchronize LDP with OSPF or IS-IS to minimize MPLS packet loss. When an IGP adjacency is established on a link but LDP-IGP synchronization is not yet achieved or is lost, the IGP will advertise the max-metric on that link.

ℹ️ Check
Review the Arista router OSPF or IS-IS configuration. ISIS configuration example: router isis 1 mpls ldp sync default OSPF configuration example: router ospf 1 mpls ldp sync default Verify LDP will synchronize with the link-state routing protocol. interface Loopback1 description MPLS-LDP-Router-ID ip address 10.1.129.94/32 mpls ldp igp sync ip ospf area 0.0.0.5 If the Arista router is not configured to synchronize IGP and LDP, this is a finding.

ℹ️ Check

Review the Arista router OSPF or IS-IS configuration. ISIS configuration example: router isis 1 mpls ldp sync default OSPF configuration example: router ospf 1 mpls ldp sync default Verify LDP will synchronize with the link-state routing protocol. interface Loopback1 description MPLS-LDP-Router-ID ip address 10.1.129.94/32 mpls ldp igp sync ip ospf area 0.0.0.5 If the Arista router is not configured to synchronize IGP and LDP, this is a finding.

✔️ Fix
Configure the Arista MPLS router to synchronize IGP and LDP, minimizing packet loss when an IGP adjacency is established prior to LDP peers completing label exchange. ISIS configuration example: P-Router-EOS(config)#router isis 1 P-Router-EOS(config-router-isis)#mpls ldp sync default OSPF configuration example: LEAF-1A(config-mpls-ldp)#router ospf 1 LEAF-1A(config-router-ospf)#mpls ldp sync default Configure LDP to synchronize with the link-state routing protocol. LEAF-1A(config)#interface Loopback1 LEAF-1A(config-if-Lo0)#erface Loopback1 LEAF-1A(config-if-Lo0)#description MPLS-LDP-Router-ID LEAF-1A(config-if-Lo0)#ip address 10.1.129.94/32 LEAF-1A(config-if-Lo0)#mpls ldp igp sync LEAF-1A(config-if-Lo0)#ip ospf area 0.0.0.5

✔️ Fix

Configure the Arista MPLS router to synchronize IGP and LDP, minimizing packet loss when an IGP adjacency is established prior to LDP peers completing label exchange. ISIS configuration example: P-Router-EOS(config)#router isis 1 P-Router-EOS(config-router-isis)#mpls ldp sync default OSPF configuration example: LEAF-1A(config-mpls-ldp)#router ospf 1 LEAF-1A(config-router-ospf)#mpls ldp sync default Configure LDP to synchronize with the link-state routing protocol. LEAF-1A(config)#interface Loopback1 LEAF-1A(config-if-Lo0)#erface Loopback1 LEAF-1A(config-if-Lo0)#description MPLS-LDP-Router-ID LEAF-1A(config-if-Lo0)#ip address 10.1.129.94/32 LEAF-1A(config-if-Lo0)#mpls ldp igp sync LEAF-1A(config-if-Lo0)#ip ospf area 0.0.0.5