IP Multicast practice questions

set routing-options multicast spt-mode disable

Why it fails: This path does not exist in Junos.

set protocols pim disable-spt-switchover

Why it fails: This is not a valid Junos configuration statement.

set protocols igmp spt-threshold 0

Why it fails: SPT threshold configuration belongs to PIM, not IGMP.

set protocols pim interface all no-bsr

Why it fails: Disabling BSR does not address register message loops.

set protocols pim rp static address 192.168.1.1 register-policy REJECT-REG

Why it fails: A register policy on the RP side filters incoming registers, but does not stop the DR from sending them initially.

set protocols pim rp static address 192.168.1.1 no-registration-suppression

Why it fails: Disabling suppression would worsen the looping by keeping registers active.

set protocols pim interface vlan.10 igmp-version 2

Why it fails: IGMP configuration belongs under [edit protocols igmp], not [edit protocols pim].

set routing-options multicast igmp-version 2 interface vlan.10

Why it fails: This is an invalid path in the Junos configuration hierarchy.

set interfaces vlan.10 igmp-version 2

Why it fails: IGMP protocol settings are defined under the routing protocols hierarchy in Junos.

set routing-options multicast rp 192.168.100.1

Why it fails: This is an invalid configuration hierarchy path in Junos.

set protocols pim static-rp address 192.168.100.1

Why it fails: The correct hierarchy uses 'rp static address', not 'static-rp address'.

set protocols igmp rp address 192.168.100.1

Why it fails: RP configuration belongs under PIM, not IGMP.

set protocols igmp import <policy-name>

Why it fails: IGMP does not use import policies for PIM join filtering.

set routing-options pim-policy <policy-name>

Why it fails: This is an invalid hierarchy path.

set interfaces all unit 0 family pim filter input <policy-name>

Why it fails: Firewall filters apply to packet data payloads, whereas PIM control traffic filtering uses PIM import policies.

set routing-options multicast pim-enable

Why it fails: This is an invalid path in Junos.

set protocols multicast enable

Why it fails: Protocols multicast does not exist as a top-level hierarchy.

set protocols pim interface all mode sparse

Why it fails: PIM sparse-mode is the default mode in Junos, so 'mode sparse' is not a valid syntax; simply enabling it on the interface is sufficient.

show msdp rpf 192.0.2.1

Why it fails: MSDP has its own peer checks, but RPF lookups for PIM use the multicast routing table verified with 'show route rpf'.

show pim rpf-table 192.0.2.1

Why it fails: This command does not exist in Junos.

show multicast rpf-failure

Why it fails: While drop counters exist, 'show route rpf' is the correct command to check the active RPF route.

MBGP unicast routing tables synchronized

Why it fails: MBGP is used for RPF checks, but the direct peer handshake relies on TCP.

PIM dense-mode adjacency between the peers

Why it fails: MSDP does not require PIM dense-mode between peers.

IGMPv3 snooping enabled on intermediate switches

Why it fails: IGMP snooping is a layer 2 feature and is not required for MSDP TCP sessions.

set routing-options msdp-policy <policy-name>

Why it fails: Routing options does not handle MSDP policy configuration.

set protocols pim msdp-import <policy-name>

Why it fails: MSDP import policies are configured under protocols msdp, not protocols pim.

set protocols bgp group msdp export <policy-name>

Why it fails: MSDP policies are configured under protocols msdp, not BGP groups.

show protocols igmp snooping vlan

Why it fails: This is an invalid operational command format in Junos.

show ethernet-switching igmp-snooping

Why it fails: While IGMP snooping relates to switching, the operational command uses 'show igmp-snooping'.

show bridge igmp-snooping querier

Why it fails: This is incorrect syntax for EX Series switches.

MSDP replaces PIM sparse-mode for forwarding multicast data traffic to receivers.

Why it fails: MSDP only shares control plane source information; PIM handles the actual data tree forwarding.

MSDP runs directly over IP protocol number 46.

Why it fails: MSDP runs over TCP (port 639), not raw IP.

IGMP snooping querier election redundancy across core switches

Why it fails: IGMP snooping querier redundancy applies to Layer 2 switch ports, not Layer 3 RP redundancy.

Static RP configuration with multiple backup RP IP addresses configured on every router

Why it fails: PIM static RP does not natively support dynamic multi-RP fallback without BSR or Anycast RP.

SSM requires PIM dense-mode to flood traffic to all routers.

Why it fails: SSM runs over PIM sparse-mode infrastructure.

SSM operates within the 224.0.0.0/24 multicast range.

Why it fails: SSM uses the 232.0.0.0/8 address range.

SSM uses (*,G) shared trees exclusively for distribution.

Why it fails: SSM builds source-specific (S,G) trees directly without shared trees.

The DR elects the IGMP querier for the VLAN segment.

Why it fails: The IGMP querier is elected independently via IGMP protocol rules, not the PIM DR election.

The DR maintains the MSDP Source-Active cache for the entire AS.

Why it fails: The MSDP Source-Active cache is maintained by MSDP-speaking routers, typically the RPs, not by a PIM DR on a multi-access segment. It is tempting because the DR does handle PIM register and join functions, but MSDP inter-domain state sits outside its role.

The DR floods all multicast traffic across the multi-access segment by default.

Why it fails: A PIM sparse-mode DR does not flood multicast traffic; it sends PIM Register messages to the RP and joins the shared tree, with traffic forwarded only to receivers that requested it. It is tempting because the DR does centralise signalling on the segment, but flooding is dense-mode behaviour.

set routing-options multicast spt-lifetime 0

Why it fails: SPT lifetime is not a valid Junos routing-options hierarchy statement for multicast.

set protocols pim switchover-delay 0

Why it fails: There is no switchover-delay statement in Junos PIM configuration.

set protocols igmp ssm-mapping

Why it fails: SSM mapping is used for translating (*,G) joins into Source-Specific Multicast joins for receivers running IGMPv2, not for SPT switchover thresholds.

Configure an RP-reachability policy under protocols pim static rp.

Why it fails: Static RP configuration does not control dynamic BSR messaging domain security.

Configure 'set protocols pim bsr-candidate interface' with a strict metric.

Why it fails: Setting a metric on a candidate-RP advertisement does not filter rogue BSR messages.

Configure a firewall filter on the loopback interface matching PIM protocol traffic destined for 224.0.0.13.

Why it fails: While this drops control plane traffic at layer 3, Junos provides a dedicated BSR boundary feature under protocols pim to suppress unauthorized BSR messages per interface.

Enable 'auto-rp compatibility' under the global [edit protocols pim] hierarchy.

Why it fails: There is no global 'auto-rp compatibility' toggle command in Junos.

Set the PIM mode to SSM-only across all core interfaces.

Why it fails: SSM does not utilize an RP, so setting SSM-only would break any sparse-mode or Auto-RP design.

Enable MSDP peering between the Auto-RP mapping agent and the Junos router.

Why it fails: MSDP is used between PIM Sparse-Mode RPs, not as a substitute for Auto-RP packet processing.

show igmp group

Why it fails: Displays locally connected IGMP membership reports.

show multicast route

Why it fails: Displays the multicast forwarding cache (mroute), but 'show pim rps' is the specific command for RP mappings.

show msdp summary

Why it fails: Shows MSDP peer status, not PIM RP information.

Configure a firewall filter family inet filter-name on the loopback interface matching destination port 639.

Why it fails: Port 639 is used for MSDP, not for filtering PIM join messages or host IGMP memberships.

Apply a bridge-domain filter under [edit bridge-domains] blocking destination MAC address 01:00:5E:00:00:01.

Why it fails: 01:00:5E:00:00:01 is the MAC address for all-hosts (224.0.0.1), blocking it would disrupt basic IP host communication entirely rather than filtering specific multicast groups.

The RP is receiving multicast traffic from the source via a shared tree that was built without the RP's involvement.

Why it fails: In PIM sparse mode, the shared tree is rooted at the RP. The RP is always involved in building the shared tree for groups for which it is the RP. Therefore, this statement is incorrect; the RP must be involved in the shared tree.

The RP is using the shortest-path tree (SPT) for the source, which bypasses the shared tree.

Why it fails: The shortest-path tree is built by the last-hop router after it receives the first packet on the shared tree. The RP itself does not switch to the SPT for the source; it remains on the shared tree unless it is also a receiver. Therefore, this does not explain the absence of (S,G) state on the RP.

The source's first-hop router is not registering with the RP because it is directly connected to the RP.

Why it fails: Even if the source's first-hop router is directly connected to the RP, PIM register messages are still sent to the RP unless the RP is also the first-hop router. However, if the RP is the first-hop router, it will have (S,G) state. This option does not correctly describe the scenario where the RP lacks (S,G) state.