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zebra: fix handle netlink state reachable message
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When creating an NHRP shortcut entry between two spokes, the cache
entry created has very often a field 'used' set to false, despite
a continuous traffic towards the 11.255.255.1 IP address.

> north-vm# show ip nhrp cache
> Iface    Type     Protocol                 NBMA                     Claimed NBMA             Flags  Identity
> gre1     local    11.255.255.2             10.125.0.2               10.125.0.2                      -
> gre1     nhs      11.255.255.1             10.125.0.1               10.125.0.1               T     west     <----

Actually, that flag reflects the protocol address reachability. A neighbor
entry is maintained in the kernel. As an ARP probe operates only with MAC
address, NHRP will take the place of ARP, and will refresh the NBMA link IP
address, every time the neighbor entry enters in PROBE state. The neighbor
entry state goes in REACHABLE state, and the expectation is that the REACHABLE
state is notified to the NHRP daemon, which does not happen.

The below dump indicates 3 netlink messages over the gre1 interface:

> # trace from 'ip monitor neigh'
> miss 11.255.255.1 dev gre1 lladdr 10.125.0.1 PROBE proto 191
> 11.255.255.1 dev gre1 lladdr 10.125.0.1 PROBE proto 191
> 11.255.255.1 dev gre1 lladdr 10.125.0.1 REACHABLE proto 191

The NHRP/ZEBRA traces indicate the first 2 netlink messages received, followed
by the update of the neighbor entry by the NHRP daemon. But there is no
reception or confirmation that the new neighbor state moved to REACHABLE.

> # trace from nhrp
> 2023/11/06 09:46:21 ZEBRA: [V8KNF-8EXH8] netlink_recv_msg: << netlink message dump [recv]
> 2023/11/06 09:46:21 ZEBRA: [JAS4D-NCWGP] nlmsghdr [len=80 type=(30) GETNEIGH flags=(0x0001) {REQUEST} seq=0 pid=0]
> 2023/11/06 09:46:21 ZEBRA: [S4WS4-PS3KF] netlink_parse_info: netlink-listen (NS 0) type RTM_GETNEIGH(30), len=80, seq=0, pid=0
> 2023/11/06 09:46:21 ZEBRA: [V8KNF-8EXH8] netlink_recv_msg: << netlink message dump [recv]
> 2023/11/06 09:46:21 ZEBRA: [JAS4D-NCWGP] nlmsghdr [len=80 type=(28) NEWNEIGH flags=(0x0000) {} seq=0 pid=0]
> 2023/11/06 09:46:21 ZEBRA: [T4YQJ-83R8H]   ndm [family=2 (AF_INET) ifindex=10 state=0x0010 {PROBE} flags=0x0000 {} type=1 (UNICAST)]
> 2023/11/06 09:46:21 ZEBRA: [KFBSR-XYJV1]     rta [len=8 (payload=4) type=(1) DST]
> 2023/11/06 09:46:21 ZEBRA: [M8QV4-KY9C0]       11.255.255.1
> 2023/11/06 09:46:21 ZEBRA: [KFBSR-XYJV1]     rta [len=8 (payload=4) type=(2) LLADDR]
> 2023/11/06 09:46:21 ZEBRA: [V74GD-NYS6Y]       0A:7D:00:01
> 2023/11/06 09:46:21 ZEBRA: [KFBSR-XYJV1]     rta [len=8 (payload=4) type=(4) PROBES]
> 2023/11/06 09:46:21 ZEBRA: [KFBSR-XYJV1]     rta [len=20 (payload=16) type=(3) CACHEINFO]
> 2023/11/06 09:46:21 ZEBRA: [KFBSR-XYJV1]     rta [len=5 (payload=1) type=(12) UNKNOWN]
> 2023/11/06 09:46:21 ZEBRA: [S4WS4-PS3KF] netlink_parse_info: netlink-listen (NS 0) type RTM_NEWNEIGH(28), len=76, seq=0, pid=0
> 2023/11/06 09:46:21 ZEBRA: [TDS34-MNEJW]     Neighbor Entry received is not on a VLAN or a BRIDGE, ignoring
> 2023/11/06 09:46:21 NHRP: [QQ0NK-1H449] Netlink: who-has 11.255.255.1 dev gre1 lladdr 10.125.0.1 nud 0x10 cache used 0 type 5
> 2023/11/06 09:46:21 NHRP: [QVXNM-NVHEQ] Netlink: update binding for 11.255.255.1 dev gre1 from c (unspec) peer.vc.nbma 10.125.0.1 to lladdr 10.125.0.1
> 2023/11/06 09:46:21 NHRP: [QQ0NK-1H449] Netlink: new-neigh 11.255.255.1 dev gre1 lladdr 10.125.0.1 nud 0x10 cache used 1 type 5
> 2023/11/06 09:46:21 ZEBRA: [NH6N7-54CD1] Tx RTM_NEWNEIGH family ipv4 IF gre1(10) Neigh 11.255.255.1 Link  10.125.0.1 flags 0x0 state 0x2 ext_flags 0x0
> 2023/11/06 09:46:21 ZEBRA: [HYEHE-CQZ9G] nl_batch_send: netlink-dp (NS 0), batch size=52, msg cnt=1

The NHRP daemon relies on zebra netlink layer. Read and write operations are
done on two different sockets. As a filter is attached to the read socket to
prevent from reading notifications from the write socket, the NEWNEIGH
operations from NHRP are ignored.

Fix this by adding an exception in the netlink filter to autorise NEWNEIGH
notifications. Consequently, the REACHABLE state is notified to NHRP.

> north-vm# show ip nhrp cache
> Iface    Type     Protocol                 NBMA                     Claimed NBMA             Flags  Identity
> gre1     local    11.255.255.2             10.125.0.2               10.125.0.2                      -
> gre1     nhs      11.255.255.1             10.125.0.1               10.125.0.1               UT     west     <----

Link: https://flylib.com/books/3/475/1/html/2/images/0131777203/graphics/15fig06.gif
Fixes: b3b7510 ("nhrpd: link layer registration to notificationas")
Signed-off-by: Philippe Guibert <[email protected]>
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@pguibert6WIND
pguibert6WIND committed Dec 15, 2023
1 parent 8efadf0 commit b42df96
Showing 1 changed file with 12 additions and 10 deletions.
22 changes: 12 additions & 10 deletions zebra/kernel_netlink.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -553,7 +553,7 @@ static void netlink_install_filter(int sock, uint32_t pid, uint32_t dplane_pid)
* nlmsg_pid == dplane_pid) {
* if (the incoming nlmsg_type ==
* RTM_NEWADDR || RTM_DELADDR || RTM_NEWNETCONF ||
* RTM_DELNETCONF)
* RTM_DELNETCONF || RTM_NEWNEIGH
* keep this message
* else
* skip this message
Expand All @@ -572,7 +572,7 @@ static void netlink_install_filter(int sock, uint32_t pid, uint32_t dplane_pid)
/*
* 2: Compare to dplane pid
*/
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, htonl(dplane_pid), 0, 6),
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, htonl(dplane_pid), 0, 7),
/*
* 3: Load the nlmsg_type into BPF register
*/
Expand All @@ -581,27 +581,29 @@ static void netlink_install_filter(int sock, uint32_t pid, uint32_t dplane_pid)
/*
* 4: Compare to RTM_NEWADDR
*/
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, htons(RTM_NEWADDR), 4, 0),
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, htons(RTM_NEWADDR), 5, 0),
/*
* 5: Compare to RTM_DELADDR
*/
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, htons(RTM_DELADDR), 3, 0),
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, htons(RTM_DELADDR), 4, 0),
/*
* 6: Compare to RTM_NEWNETCONF
*/
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, htons(RTM_NEWNETCONF), 2,
0),
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, htons(RTM_NEWNETCONF), 3, 0),
/*
* 7: Compare to RTM_DELNETCONF
*/
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, htons(RTM_DELNETCONF), 1,
0),
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, htons(RTM_DELNETCONF), 2, 0),
/*
* 8: This is the end state of we want to skip the
* 8: Compare to RTM_NEWNEIGH
*/
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, htons(RTM_NEWNEIGH), 1, 0),
/*
* 9: This is the end state of we want to skip the
* message
*/
BPF_STMT(BPF_RET | BPF_K, 0),
/* 9: This is the end state of we want to keep
/* 10: This is the end state of we want to keep
* the message
*/
BPF_STMT(BPF_RET | BPF_K, 0xffff),
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