问题描述
现场同时开启了nat alg h323和nat alg sip，h323业务正常，但sip业务不正常。
防火墙上做了nat。由内发起的报文源为10.129.Y.Y, 目的为2.32.Z.Z，源IP过防火墙被转成2.32.X.X。
interface Vlan-interface1197
nat outbound 3000 port-preserved
nat server protocol udp global 2.32.X.X 5060 inside 10.129.Y.Y 5060 rule ServerRule_8
过程分析
通过在防火墙上debug看 报文上墙后正常转发：
*Dec 5 16:35:57:304 2024 视频专网防火墙 IPFW/7/IPFW_PACKET:
Receiving, interface = Route-Aggregation28
version = 4, headlen = 20, tos = 16
pktlen = 61, pktid = 13158, offset = 0, ttl = 63, protocol = 17
checksum = 32034, s = 10.129.Y.Y, d = 2.32.Z.Z
channelID = 0, vpn-InstanceIn = 0, vpn-InstanceOut = 0.
VsysID = 1
prompt: Receiving IP packet from interface Route-Aggregation28.
Payload: UDP
source port = 5060, destination port = 5060
checksum = 0x5746, length = 41.
*Dec 5 16:35:57:304 2024 视频专网防火墙 IPFW/7/IPFW_INFO:
MBUF was intercepted! Phase Num is 3(post routing), Service ID is 7(rir), Bitmap is 100000000000000, return 0(0:continue, 1:dropped, 2:consumed, 3:enqueued, 4:relay)! Interface is Route-Aggregation28,……
*Dec 5 16:35:57:304 2024 视频专网防火墙 SESSION/7/TABLE:
Tuple5(EVENT): 10.129.Y.Y/5060-->2.32.X.X/5060(UDP(17))
Session entry was created.
*Dec 5 16:35:57:304 2024 视频专网防火墙 FILTER/7/PACKET: The packet is permitted. ……
看NAT源IP有转换，且应用层也有过ALG转换：
*Dec 5 16:35:57:304 2024 视频专网防火墙 NAT/7/COMMON:
PACKET: (Vlan-interface1197-out-config) Protocol: UDP
10.129.X.X:5060 - 2.32.Z.Z:5060(VPN: 0)(vsys: 1) ------>
2.32.X.X:21144 - 2.32.Z.Z:5060(VPN: 0)(vsys: 1)
*Dec 5 16:36:01:107 2024 视频专网防火墙 NAT/7/ALG:
PACKET: (Vlan-interface1197) ALG payload was translated according to session table(Src):
10.129.Y.Y/5060(VPN: 0) ---> 2.32.X.X/5060(VPN: 0)
*Dec 5 16:36:01:107 2024 视频专网防火墙 NAT/7/ALG:
PACKET: (ifIndex:0) ALG payload was translated according to session table(Dst-by-L3Head):
2.32.Z.Z/5060(VPN: 0) ---> 2.32.Z.Z/5060(VPN: 0)
看抓包也是正常的：
解决方法
尝试在防火墙上加上session alg fragment sip后正常。
后续现场询问SIP业务服务器侧确实有分片需求。