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Cisco Bug: CSCvv01250 - IGMP reports are forwarded to mrouter port untagged regardless of which VLAN the group is in

Last Modified

Oct 14, 2020

Products (1)

  • Cisco 1000 Series Integrated Services Routers

Known Affected Releases

16.9.5

Description (partial)

Symptom:
When igmp snooping is enabled and connection between PE router and C1117 is done via trunk interface, igmp packets are sent from C1117 and PE router is able to receive it, however the frame is coming without dot1q header


IGMP SNOOPING ENABLED ? Packet received in C9300 from C1117

Frame 63: 60 bytes on wire (480 bits), 60 bytes captured (480 bits) on interface 0
    Interface id: 0 (/tmp/epc_ws/wif_to_ts_pipe)
    Encapsulation type: Ethernet (1)
    Arrival Time: Jun 22, 2020 07:44:02.259075000 UTC
    [Time shift for this packet: 0.000000000 seconds]
    Epoch Time: 1592811842.259075000 seconds
    [Time delta from previous captured frame: 0.422818000 seconds]
    [Time delta from previous displayed frame: 0.000000000 seconds]
    [Time since reference or first frame: 52.516730000 seconds]
    Frame Number: 63
    Frame Length: 60 bytes (480 bits)
    Capture Length: 60 bytes (480 bits)
    [Frame is marked: False]
    [Frame is ignored: False]
    [Protocols in frame: eth:ethertype:ip:igmp:igmp]
Ethernet II, Src: 70:6d:15:f0:1e:82 (70:6d:15:f0:1e:82), Dst: 01:00:5e:01:01:01 (01:00:5e:01:01:01)
    Destination: 01:00:5e:01:01:01 (01:00:5e:01:01:01)
        Address: 01:00:5e:01:01:01 (01:00:5e:01:01:01)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
        .... ...1 .... .... .... .... = IG bit: Group address (multicast/broadcast)
    Source: 70:6d:15:f0:1e:82 (70:6d:15:f0:1e:82)
        Address: 70:6d:15:f0:1e:82 (70:6d:15:f0:1e:82)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)                                                                                                                            <-- No dot1q header
    Type: IPv4 (0x0800)
    Padding: 0000000000000000000000000000

Internet Protocol Version 4, Src: 10.1.1.100, Dst: 234.xxx.xxx.xxx
    0100 .... = Version: 4
    .... 0110 = Header Length: 24 bytes (6)
    Differentiated Services Field: 0xc0 (DSCP: CS6, ECN: Not-ECT)
        1100 00.. = Differentiated Services Codepoint: Class Selector 6 (48)
        .... ..00 = Explicit Congestion Notification: Not ECN-Capable Transport (0)
    Total Length: 32
    Identification: 0x006e (110)
    Flags: 0x00
        0... .... = Reserved bit: Not set
        .0.. .... = Don't fragment: Not set
        ..0. .... = More fragments: Not set
    Fragment offset: 0
    Time to live: 1
    Protocol: IGMP (2)
    Header checksum: 0x2d43 [validation disabled]
        [Good: False]
        [Bad: False]
    Source: 10.1.1.100
    Destination: 234.xxx.xxx.xxx
    Options: (4 bytes), Router Alert
        Router Alert (4 bytes): Router shall examine packet (0)
            Type: 148
                1... .... = Copy on fragmentation: Yes
                .00. .... = Class: Control (0)
                ...1 0100 = Number: Router Alert (20)
            Length: 4
            Router Alert: Router shall examine packet (0)
Internet Group Management Protocol
    [IGMP Version: 2]
    Type: Membership Report (0x16)
    Max Resp Time: 0.0 sec (0x00)
    Header checksum: 0xfefc [correct]
    Multicast Address: 234.xxx.xxx.xxx

==================================================================================

When igmp snooping is disabled in C1117 we see below behavior:

IGMP SNOOPING DISABLED ? Packet received in C9300 from C1117

Frame 194: 64 bytes on wire (512 bits), 64 bytes captured (512 bits) on interface 0
    Interface id: 0 (/tmp/epc_ws/wif_to_ts_pipe)
    Encapsulation type: Ethernet (1)
    Arrival Time: Jun 22, 2020 07:56:01.641070000 UTC
    [Time shift for this packet: 0.000000000 seconds]
    Epoch Time: 1592812561.641070000 seconds
    [Time delta from previous captured frame: 0.967733000 seconds]
    [Time delta from previous displayed frame: 0.000000000 seconds]
    [Time since reference or first frame: 156.449488000 seconds]
    Frame Number: 194
    Frame Length: 64 bytes (512 bits)
    Capture Length: 64 bytes (512 bits)
    [Frame is marked: False]
    [Frame is ignored: False]
    [Protocols in frame: eth:ethertype:vlan:ethertype:ip:igmp:igmp]
Ethernet II, Src: 70:6d:15:f0:1e:82 (70:6d:15:f0:1e:82), Dst: 01:00:5e:01:01:01 (01:00:5e:01:01:01)
    Destination: 01:00:5e:01:01:01 (01:00:5e:01:01:01)
        Address: 01:00:5e:01:01:01 (01:00:5e:01:01:01)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
        .... ...1 .... .... .... .... = IG bit: Group address (multicast/broadcast)
    Source: 70:6d:15:f0:1e:82 (70:6d:15:f0:1e:82)
        Address: 70:6d:15:f0:1e:82 (70:6d:15:f0:1e:82)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
    Type: 802.1Q Virtual LAN (0x8100)
802.1Q Virtual LAN, PRI: 0, CFI: 0, ID: 1331                                           <-- Correct dot1q header
    000. .... .... .... = Priority: Best Effort (default) (0)
    ...0 .... .... .... = CFI: Canonical (0)
    .... 0101 0011 0011 = ID: 1331
    Type: IPv4 (0x0800)
    Padding: 00000000000000000000
    Trailer: 00000000
Internet Protocol Version 4, Src: 10.1.1.100, Dst: 234.xxx.xxx.xxx
    0100 .... = Version: 4
    .... 0110 = Header Length: 24 bytes (6)
    Differentiated Services Field: 0xc0 (DSCP: CS6, ECN: Not-ECT)
        1100 00.. = Differentiated Services Codepoint: Class Selector 6 (48)
        .... ..00 = Explicit Congestion Notification: Not ECN-Capable Transport (0)
    Total Length: 32
    Identification: 0x0089 (137)
    Flags: 0x00
        0... .... = Reserved bit: Not set
        .0.. .... = Don't fragment: Not set
        ..0. .... = More fragments: Not set
    Fragment offset: 0
    Time to live: 1
    Protocol: IGMP (2)
    Header checksum: 0x2d28 [validation disabled]
        [Good: False]
        [Bad: False]
    Source: 10.1.1.100
    Destination: 234.xxx.xxx.xxx
    Options: (4 bytes), Router Alert
        Router Alert (4 bytes): Router shall examine packet (0)
            Type: 148
                1... .... = Copy on fragmentation: Yes
                .00. .... = Class: Control (0)
                ...1 0100 = Number: Router Alert (20)
            Length: 4
            Router Alert: Router shall examine packet (0)
Internet Group Management Protocol
    [IGMP Version: 2]
    Type: Membership Report (0x16)
    Max Resp Time: 0.0 sec (0x00)
    Header checksum: 0xfefc [correct]
    Multicast Address: 234.xxx.xxx.xxx


If we change the trunk port to an access port, multicast starts to work with IGMP snooping enabled.

Conditions:
Igmp snooping enabled in C1117. A integrated switch port in trunk mode  is configured as the mrouter port of specific VLAN. This VLAN id is not the native VLAN id of this trunk port.
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