STIGQter: STIG Summary: Cisco NX-OS Switch RTR Security Technical Implementation Guide Version: 2 Release: 1 Benchmark Date: 23 Apr 2021:

The Cisco multicast Rendezvous Point (RP) switch must be configured to limit the multicast forwarding cache so that its resources are not saturated by managing an overwhelming number of Protocol Independent Multicast (PIM) and Multicast Source Discovery Protocol (MSDP) source-active entries.

DISA Rule

SV-221135r622190_rule

Vulnerability Number

V-221135

Group Title

SRG-NET-000362-RTR-000120

Rule Version

CISC-RT-000820

Severity

CAT III

CCI(s)

• CCI-002385 - The information system protects against or limits the effects of organization-defined types of denial of service attacks by employing organization-defined security safeguards.

Weight

10

Fix Recommendation

The risk associated with this requirement can be fully mitigated by configuring the switch to filter PIM register messages, rate limiting the number of PIM register messages, and accept MSDP packets only from known MSDP peers.

Step 1: Configure the switch to filter PIM register messages received from a multicast DR for any undesirable multicast groups and sources. The example below will deny any multicast streams for groups 239.5.0.0/16 and allow from only sources x.1.2.6 and x.1.2.7.

Step 1a: Configure a route map to filter multicast groups and sources as shown in the example below:

SW1(config)# route-map PIM_REGISTER_FILTER deny 10
SW1(config-route-map)# match ip multicast group 239.5.0.0/16
SW1(config-route-map)# route-map PIM_REGISTER_FILTER permit 20
SW1(config-route-map)# match ip multicast source x.1.2.6/32
SW1(config-route-map)# route-map PIM_REGISTER_FILTER permit 30
SW1(config-route-map)# match ip multicast source x.1.2.7/32
SW1(config-route-map)# route-map PIM_REGISTER_FILTER permit 40
SW1(config-route-map)# match ip multicast group-range 232.0.0.0 to 233.255.255.255
SW1(config-route-map)# route-map PIM_REGISTER_FILTER deny 50
SW1(config-route-map)# match ip multicast source 0.0.0.0/0
SW1(config-route-map)# exit

Step 1b: Configure a multicast register policy referencing the configured route map.

SW1(config)# ip pim register-policy PIM_REGISTER_FILTER
SW1(config)# end

Step 2: Configure the receive path or interface ACLs to only accept MSDP packets from known MSDP peers.

SW1(config)# ip access-list EXTERNAL_ACL_INBOUND
SW1(config-acl) # permit tcp any any established
SW1(config-acl) # permit tcp host x.1.28.2 host x.1.28.8 eq 639
SW1(config-acl) # deny tcp any host x1.28.8 eq 639
SW1(config-acl) # permit tcp host x.1.28.2 host x.1.28.8 eq bgp
SW1(config-acl) # permit tcp host x.1.28.2 eq bgp host x.1.28.8
SW1(config-acl) # permit pim host x.1.28.2 host x.1.28.8
…
…
…
SW1(config-acl)# deny ip any any

Check Contents

The Cisco switch does not have a mechanism to limit the multicast forwarding cache. However, the risk associated with this requirement can be fully mitigated by configuring the switch to filter PIM register messages and accept MSDP packets only from known MSDP peers.

Step 1: Verify that the RP is configured to filter PIM register messages for any undesirable multicast groups and sources. The example below will deny any multicast streams for groups 239.5.0.0/16 and allow from only sources x.1.2.6 and x.1.2.7.

ip pim register-policy PIM_REGISTER_FILTER
…
…
…
route-map PIM_REGISTER_FILTER deny 10
match ip multicast group 239.5.0.0/16
route-map PIM_REGISTER_FILTER permit 20
match ip multicast source x.1.2.6/32
route-map PIM_REGISTER_FILTER permit 30
match ip multicast source x.1.2.7/32
route-map PIM_REGISTER_FILTER permit 40
match ip multicast group-range 232.0.0.0 to 233.255.255.255
route-map PIM_REGISTER_FILTER deny 50
match ip multicast source 0.0.0.0/0

Step 2: Review the switch configuration to determine if there is a receive path or interface filter to only accept MSDP packets from known MSDP peers as shown in the example below.

Step 2a: Verify that interfaces used for MSDP peering have an inbound ACL as shown in the example.

interface Ethernet2/3
no switchport
ip access-group EXTERNAL_ACL_INBOUND in
ip address x.1.28.8/24
ip pim sparse-mode

Step 2b: Verify that the ACL restricts MSDP peering to only known sources.

ip access-list EXTERNAL_ACL_INBOUND
10 permit tcp any any established
20 permit tcp x.1.28.2/32 x.1.28.8/32 eq 639
30 deny tcp any x.1.28.8/32 eq 639 log
40 permit tcp x.1.28.2/32 10.x.28.8/32 eq bgp
50 permit tcp x.1.28.2/32 eq bgp x.1.28.8/32
60 permit pim x.1.28.2/32 x.1.28.8/32
…
…
…
120 deny ip any any log

Note: MSDP connections is via TCP port 639.

If the RP switch is not configured to filter PIM register messages and accept MSDP packets only from known MSDP peers, this is a finding.

Vulnerability Number

V-221135

Documentable

False

Rule Version

CISC-RT-000820

Severity Override Guidance

The Cisco switch does not have a mechanism to limit the multicast forwarding cache. However, the risk associated with this requirement can be fully mitigated by configuring the switch to filter PIM register messages and accept MSDP packets only from known MSDP peers.

Step 1: Verify that the RP is configured to filter PIM register messages for any undesirable multicast groups and sources. The example below will deny any multicast streams for groups 239.5.0.0/16 and allow from only sources x.1.2.6 and x.1.2.7.

ip pim register-policy PIM_REGISTER_FILTER
…
…
…
route-map PIM_REGISTER_FILTER deny 10
match ip multicast group 239.5.0.0/16
route-map PIM_REGISTER_FILTER permit 20
match ip multicast source x.1.2.6/32
route-map PIM_REGISTER_FILTER permit 30
match ip multicast source x.1.2.7/32
route-map PIM_REGISTER_FILTER permit 40
match ip multicast group-range 232.0.0.0 to 233.255.255.255
route-map PIM_REGISTER_FILTER deny 50
match ip multicast source 0.0.0.0/0

Step 2: Review the switch configuration to determine if there is a receive path or interface filter to only accept MSDP packets from known MSDP peers as shown in the example below.

Step 2a: Verify that interfaces used for MSDP peering have an inbound ACL as shown in the example.

interface Ethernet2/3
no switchport
ip access-group EXTERNAL_ACL_INBOUND in
ip address x.1.28.8/24
ip pim sparse-mode

Step 2b: Verify that the ACL restricts MSDP peering to only known sources.

ip access-list EXTERNAL_ACL_INBOUND
10 permit tcp any any established
20 permit tcp x.1.28.2/32 x.1.28.8/32 eq 639
30 deny tcp any x.1.28.8/32 eq 639 log
40 permit tcp x.1.28.2/32 10.x.28.8/32 eq bgp
50 permit tcp x.1.28.2/32 eq bgp x.1.28.8/32
60 permit pim x.1.28.2/32 x.1.28.8/32
…
…
…
120 deny ip any any log

Note: MSDP connections is via TCP port 639.

If the RP switch is not configured to filter PIM register messages and accept MSDP packets only from known MSDP peers, this is a finding.

Check Content Reference

M

Target Key

4075

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