The MPLS router with RSVP-TE enabled must be configured with message pacing to adjust maximum burst and maximum number of RSVP messages to an output queue based on the link speed and input queue size of adjacent core routers.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-78289	SRG-NET-000193-RTR-000001	SV-92995r1_rule		Low

Description
RSVP-TE can be used to perform constraint-based routing when building LSP tunnels within the network core that will support QoS and traffic engineering requirements. RSVP-TE is also used to enable MPLS Fast Reroute, a network restoration mechanism that will reroute traffic onto a backup LSP in case of a node or link failure along the primary path. When there is a disruption in the MPLS core, such as a link flap or router reboot, the result is a significant amount of RSVP signaling, such as "PathErr" and "ResvErr" messages that need to be sent for every LSP using that link. When RSVP messages are sent out, they are sent either hop by hop or with the router alert bit set in the IP header. This means that every router along the path must examine the packet to determine if additional processing is required for these RSVP messages. If there is enough signaling traffic in the network, it is possible for an interface to receive more packets for its input queue than it can hold, resulting in dropped RSVP messages and hence slower RSVP convergence. Increasing the size of the interface input queue can help prevent dropping packets; however, there is still the risk of having a burst of signaling traffic that can fill the queue. The best solution is RSVP message pacing to control the rate at which RSVP messages are sent so the input queue on the other end of the link is not overloaded.

Description

RSVP-TE can be used to perform constraint-based routing when building LSP tunnels within the network core that will support QoS and traffic engineering requirements. RSVP-TE is also used to enable MPLS Fast Reroute, a network restoration mechanism that will reroute traffic onto a backup LSP in case of a node or link failure along the primary path. When there is a disruption in the MPLS core, such as a link flap or router reboot, the result is a significant amount of RSVP signaling, such as "PathErr" and "ResvErr" messages that need to be sent for every LSP using that link. When RSVP messages are sent out, they are sent either hop by hop or with the router alert bit set in the IP header. This means that every router along the path must examine the packet to determine if additional processing is required for these RSVP messages. If there is enough signaling traffic in the network, it is possible for an interface to receive more packets for its input queue than it can hold, resulting in dropped RSVP messages and hence slower RSVP convergence. Increasing the size of the interface input queue can help prevent dropping packets; however, there is still the risk of having a burst of signaling traffic that can fill the queue. The best solution is RSVP message pacing to control the rate at which RSVP messages are sent so the input queue on the other end of the link is not overloaded.

STIG	Date
Router Security Requirements Guide	2018-01-26

Details

Check Text ( C-77847r1_chk )
Review the router configuration to verify that the router has been configured to prevent a burst of RSVP traffic engineering signaling messages from overflowing the input queue of any neighbor core router. If the router with RSVP-TE enabled does not have message pacing configured based on the link speed and input queue size of adjacent core routers, this is a finding.

Fix Text (F-85017r1_fix)
Ensure all routers with RSVP-TE enabled have message pacing configured that will adjust maximum burst and maximum number of RSVP messages to an output queue based on the link speed and input queue size of adjacent core routers.