The Arista multicast router must be configured to disable Protocol Independent Multicast (PIM) on all interfaces that are not required to support multicast routing.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-255998	ARST-RT-000120	SV-255998r882336_rule		Medium

Description

If multicast traffic is forwarded beyond the intended boundary, it is possible that it can be intercepted by unauthorized or unintended personnel. Limiting where, within the network, a given multicast group's data is permitted to flow is an important first step in improving multicast security. A scope zone is an instance of a connected region of a given scope. Zones of the same scope cannot overlap while zones of a smaller scope will fit completely within a zone of a larger scope. For example, Admin-local scope is smaller than Site-local scope, so the administratively configured boundary fits within the bounds of a site. According to RFC 4007 IPv6 Scoped Address Architecture (section 5), scope zones are also required to be "convex from a routing perspective"; that is, packets routed within a zone must not pass through any links that are outside of the zone. This requirement forces each zone to be one contiguous island rather than a series of separate islands. As stated in the DOD IPv6 IA Guidance for MO3, "One should be able to identify all interfaces of a zone by drawing a closed loop on their network diagram, engulfing some routers and passing through some routers to include only some of their interfaces." Therefore, it is imperative that the network engineers have documented their multicast topology and thereby knows which interfaces are enabled for multicast. Once this is done, the zones can be scoped as required.

STIG	Date
Arista MLS EOS 4.2x Router Security Technical Implementation Guide	2023-01-17

Details

Check Text ( C-59674r882334_chk )

If IPv4 or IPv6 multicast routing is enabled on the Arista router, verify all interfaces enabled for PIM are documented in the network's multicast topology diagram. Review the Arista router configuration to determine which interfaces are enabled for PIM, identified via the "pim ipv4 sparse-mode" for ipv4 and "pim ipv6 sparse-mode" for ipv6 statement in the interface configuration, and compare to the topology. sh run | sec pim interface Ethernet3 pim ipv4 sparse-mode interface Ethernet8 pim ipv4 sparse-mode pim ipv6 sparse-mode interface Ethernet9 pim ipv4 sparse-mode pim ipv6 sparse-mode interface Vlan8 pim ipv4 sparse-mode If an interface is not required to support multicast routing and it is enabled, this is a finding.

Fix Text (F-59617r882335_fix)

Document all enabled interfaces for PIM in the network's multicast topology diagram. Disable support for PIM on interfaces that are not required to support it. Step 1: Configure the router in global configuration mode to support multicast routing. router(config)#router multicast router(config-router-multicast)#ipv4 router(config-router-multicast-ipv4)#routing router(config-router-multicast-ipv4)#exit router(config-router-multicast)#exit Step 2: Enable PIM on interfaces required to support multicast. Interfaces have PIM disabled by default. To enable PIM from an interface active in a multicast network, enter "pim sparse-mode" in the interface configuration mode. router(config)#interface Ethernet1 router(config-if-Et1)#pim ipv4 sparse-mode router(config-if-Et1)#pim ipv6 sparse-mode Step 3: Disable support for PIM on interfaces that are not required to support it. router(config)#interface Ethernet2 router(config-if-Et2)#no pim ipv4 sparse-mode router(config-if-Et2)#no pim ipv6 sparse-mode