Independent Submission W. Zhou Request for Comments: 7910 Cisco Systems Category: Informational June 2016 ISSN: 2070-1721Interoperability between the Virtual Router Redundancy Protocol and PIM
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RFC 7910 VRRP PIM Interoperability June 2016
Table of Contents
1. Introduction
The Virtual Router Redundancy Protocol (VRRP) [RFC5798] is a redundancy protocol for establishing a fault-tolerant default router. The protocol establishes a framework between network devices in order to achieve default device failover if the primary devices become inaccessible.
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RFC 7910 VRRP PIM Interoperability June 2016 2. Tracking and FailoverWithout the mechanisms described in this document, a PIM component will send PIM J/P messages with the DR's IP address to upstream routers. A GenID (Generation Identifier) in a PIM Hello message is randomly selected when the router boots and remains the same as long as the router is up. A PIM neighbor reboot can easily be detected if its GenID is different from before; in this case, the PIM J/P and RP-Set information can be redistributed to the rebooted neighbor. With the VRRP-aware PIM mechanism enabled, the PIM component listens to the state-change notifications from VRRP and automatically adjusts the priority of the PIM DR based on the VRRP state and ensures the VRRP MR (if there is only one VRRP group) becomes the DR of the LAN. If there are multiple VRRP groups, the DR is determined by the user- configured priority value.
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RFC 7910 VRRP PIM Interoperability June 2016
Alternatively, the implementation can choose to have all VRRP passive routers maintain mroute states and record the GenID of the current MR. When a passive router becomes the MR, it uses the existing mroute states and the recorded MR GenID in its PIM Hello message. This will avoid resending PIM J/P messages upon failover and will eliminate the requirement of an additional PIM Hello with vIP. There is no change in on-the-wire behavior or in the PIM and VRRP message format.
3. PIM Assert Metric Auto-Adjustment
It is possible that, after the VRRP MR switches from router A to B, A would still forward multicast traffic, which will result in duplicate traffic. The PIM Assert mechanism will kick in because PIM Assert with redundancy is enabled.
4. DF Election for BiDir Group
Change to Designated Forwarder (DF) offer/winner metric is handled similarly to PIM Assert handling with VRRP.
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RFC 7910 VRRP PIM Interoperability June 2016
o If there is at least one VRRP group in Active state, then the original offer metric preference to RP will be used. That is, the winner will be selected between routers using their real offer metric, as if no VRRP is involved.
5. Tracking Multiple VRRP Groups on an Interface
A user can configure a PIM component to track more than one VRRP groups on an interface. This allows other applications to exploit PIM/VRRP interoperability to achieve various goals (e.g., load balancing). Since each VRRP group that is configured on an interface could be in different states at any moment, the DR priority is adjusted. The PIM Assert metric and PIM BiDir DF metric should be adjusted if and only if all VRRP groups that are configured on an interface are in Passive (non-Active) states to ensure that interfaces with all-passive VRRP groups do not win DR, Assert, and DF election. In other words, the DR, Assert, and DF winners will be elected among the interfaces with at least one active VRRP group.
6. Support of HSRP
Although there are differences between VRRP and the Hot Standby Router Protocol (HSRP) [RFC2281] -- including the number of backup (standby) routers, virtual IP address, and timer intervals -- the proposed scheme can also enable HSRP-aware PIM with similar failover and the tracking mechanism described in this document.
7. Security Considerations
The proposed tracking mechanism does not discuss adding authentication to the protocols and introduces no new negative impact or threats on security to PIM in either SSM (Source-Specific Multicast) or ASM (Any-Source Multicast) mode. Note that VRRP messages from malicious nodes could cause unexpected behaviors such as multiple MRs and PIM DRs, which are associated with VRRP-specific security issues. To mitigate the vulnerability of frequent VRRP and PIM DR state change from malicious attack, an implementation can choose to enable VRRP preemption such that a higher-priority VRRP backup router does not take over for a lower-priority MR; this will reduce the state-change notifications to a PIM component and subsequent mroute state changes. Detailed analysis of PIM and VRRP security is provided in [RFC5294] and [RFC5798].
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RFC 7910 VRRP PIM Interoperability June 2016 8. Informative References[RFC2281] Li, T., Cole, B., Morton, P., and D. Li, "Cisco Hot
