P25nx

troubleshooting

The P25nx network sends to multicast and there can only be one multicast talker at a time.

From time to time it will loop, generally due to misconfiguration on a given client. This will present double the packets on the receiving multicast interface and generally cause the ducks screwing noise.

To deal with this, you must find the user doing the looping and null route them.

To find if this is an issue use the following command:

   sh ip mfib active 2
   Active Multicast Sources - sending >= 2 kbps
   Default
   Group: 239.1.0.1   << This is the World Wide Group 10100 multicast IP
     Source: 172.31.4.102,  << the known node
       SW Rate: 48 pps/20 kbps(1sec), 2 kbps(last 581 sec)
     Source: 172.31.4.110', << the looper
       SW Rate: 45 pps/19 kbps(1sec), 4 kbps(last 1219 sec)

Normally if things are working you may see senders cached, if there is a fast back and forth. However in a quiet network, you should only see one sender on a given multicast destination IP. Wait until there is no activity and then key your known node. In the above case, the known node is 172.31.4.110.

Verify this a few times, and then ensure that is truly one node.

As we have DMVPN running, this route will be to a private IP on Tunnel0, use the Show IP route command

   sh ip route 172.31.4.110
   Routing entry for 172.31.4.108/30
     Known via "ospf 1", distance 110, metric 101, type intra area
     Last update from 172.21.4.76 on Tunnel0, 19:25:20 ago
     Routing Descriptor Blocks:
     * 172.21.4.76, from 10.2.4.76, 19:25:20 ago, via Tunnel0
         Route metric is 101, traffic share count is 1

172.21.4.76 is the senders interface on Tunnel0 10.2.4.76 is the sender's router loopback

To map this to the public IP use "sh ip nhrp

   sh ip nhrp 172.21.4.76
    172.21.4.76/32 via 172.21.4.76
      Tunnel0 created 19:50:05, expire 00:09:49
      Type: dynamic, Flags: unique registered used 
      NBMA address: 104.187.150.145     
        (Claimed NBMA address: 192.168.2.4)

104.187.150.145 is the users public IP, and you can see they are behind NAT as the users router is claiming it's public IP is 192.168.2.4

Null routing that public IP will block them from the network ip route 104.187.150.145 255.255.255.255 Null0

However this will not allow access into that router, and you can keep the router access open by just null routing the IP of the sender

   ip route 172.31.4.110 255.255.255.255 null0

There are three formats for the p25 network packet. All ride inside of a UDP packet

Version 3

This is the development version of the packet and is not to be used as it's pre-standard. This should support IPv4 unicast and Multicast transports. multicast will be the primary transport focused on.

IPv4 Pseudo Header Format

Offsets	Octet	0								1								2								3
Octet	Bit	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
0	0	Source IPv4 Address
4	32	Destination IPv4 Address
8	64	Zeroes								Protocol								UDP Length
12	96	Source Port																Destination Port
16	128	Length																Checksum
20	160+	Data