On my Fedora 34 Linux firewall/router box I noticed
- that IPV6 DHCP PD requests are sent out fine.
- that IPV6 DHCP PD replies do arrive on the wire
- that the firewall kernel for some reason sends the DHCP PD reply in the FORWARD rule even though dhclient is local
- that addresses in the packets were correct, match with DHCP-server and local firewall.
Details can be found at redhat.
We have a ppp interface:
# ip -6 a s dev ppp0
20: ppp0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1492 qdisc cbq state UNKNOWN group default qlen 3
inet6 fe80::c5d5:e942:39c7:7eb7 peer fe80::9ecc:83ff:fec6:e7e5/128 scope link
valid_lft forever preferred_lft forever
We have dhclient listening at ppp0:
# lsof -p 4066992 -n
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
dhclient 4066992 root cwd DIR 254,0 4096 40961 /root
dhclient 4066992 root rtd DIR 254,0 4096 2 /
dhclient 4066992 root txt REG 254,2 2018144 141553 /usr/sbin/dhclient
dhclient 4066992 root mem REG 254,2 53728 22104 /usr/lib64/libnss_files-2.33.so
dhclient 4066992 root mem REG 254,2 1913544 21939 /usr/lib64/libc-2.33.so
dhclient 4066992 root mem REG 254,2 32696 30196 /usr/lib64/libcap-ng.so.0.0.0
dhclient 4066992 root mem REG 254,2 842360 30776 /usr/lib64/ld-2.33.so
dhclient 4066992 root 0u CHR 136,4 0t0 7 /dev/pts/4 (deleted)
dhclient 4066992 root 1u CHR 136,4 0t0 7 /dev/pts/4 (deleted)
dhclient 4066992 root 2u CHR 136,4 0t0 7 /dev/pts/4 (deleted)
dhclient 4066992 root 3u unix 0x000000001f2593f7 0t0 16525445 type=DGRAM (UNCONNECTED)
dhclient 4066992 root 4w REG 254,4 64 251 /var/lib/dhclient/dhclient6.leases
dhclient 4066992 root 5w FIFO 0,8 0t0 16525446 pipe
dhclient 4066992 root 6u IPv6 16524541 0t0 UDP [fe80::c5d5:e942:39c7:7eb7]:dhcpv6-client
That appears to be all correct.
Then the packets that come in:
# tcpdump -i ppp0 -vn port 546
dropped privs to tcpdump
tcpdump: listening on ppp0, link-type LINUX_SLL (Linux cooked v1), snapshot length 262144 bytes
06:53:09.236781 IP6 (flowlabel 0x7f0d8, hlim 1, next-header UDP (17) payload length: 60) fe80::c5d5:e942:39c7:7eb7.dhcpv6-client > ff02::1:2.dhcpv6-server: [udp sum ok] dhcp6 solicit (xid=b68ba1 (client-ID hwaddr/time type 1 time 394565497 004063f60200) (option-request DNS-server DNS-search-list) (elapsed-time 65535) (IA_PD IAID:0 T1:3600 T2:5400))
06:53:09.469530 IP6 (class 0xc0, hlim 64, next-header UDP (17) payload length: 141) fe80::9ecc:83ff:fec6:e7e5.dhcpv6-server > fe80::c5d5:e942:39c7:7eb7.dhcpv6-client: [udp sum ok] dhcp6 advertise (xid=b68ba1 (client-ID hwaddr/time type 1 time 394565497 004063f60200) (server-ID vid 0000058339633a63) (IA_PD IAID:0 T1:3600 T2:5760 (IA_PD-prefix 2001:981:a812::/48 pltime:7200 vltime:7200)) (DNS-server 2001:888:0:6::66 2001:888:0:9::99))
06:53:09.469756 IP6 (class 0xc0, hlim 63, next-header UDP (17) payload length: 141) fe80::9ecc:83ff:fec6:e7e5.dhcpv6-server > fe80::c5d5:e942:39c7:7eb7.dhcpv6-client: [udp sum ok] dhcp6 advertise (xid=b68ba1 (client-ID hwaddr/time type 1 time 394565497 004063f60200) (server-ID vid 0000058339633a63) (IA_PD IAID:0 T1:3600 T2:5760 (IA_PD-prefix 2001:981:a812::/48 pltime:7200 vltime:7200)) (DNS-server 2001:888:0:6::66 2001:888:0:9::99))
^C
Appear to be addressed correctly, to the dhclient interface.
So why doesn't dhclient receive?
I did test without an active firewall: no change.
I simplified routing, etc but no change.
It is not the problem from https://stackoverflow.com/questions/19702489/response-udp-packets-not-arriving-regardless-of-right-ip-and-port-after-sending as the dhcp-server can be contacted due to the routes present.
Where do I look to find out why a DHCP reply packet with a PD in it does not arrive locally?
Please post.
Udo
