Common Address Redundancy Protocol (CARP) sample
Packet format:
| field# | bits | Description |
|---|---|---|
| version | 4 | The version of the CARP protocol.This is statically defined as 2 in the header file /usr/src/netinet/ip_carp.h. |
| type | 4 | The type field defines the type of CARP packet. This value can be 0x01 (advertisement) or 0x02 (leave group), but the latter is only defined in the header file; I have not seen it being used anywhere. |
| vhid | 8 | Virtual host id. |
| advskew | 8 | Advertisement skew. |
| authlen | 8 | Size of Counter field + md field in 32 bit chunks.Statically defined as 7 in the header file. |
| Pad1 | 8 | Unused, must be 0. |
| advbase | 8 | Advertisement interval. |
| cksum | 16 | Checksum for Internet Protocol family headers. |
| counter | 64 | Two counters used for replay detection.(not implemented yet) |
| Md | 160 | SHA-1 HMAC generated with the passparameter as secret key, and counter, version, type, vhid, and virtual IP address as the message digest |
read more at https://www.giac.org/paper/gsec/4031/carp-free-fail-over-protocol/106433
Configuration:
VHID: 1 Advbase: 1 Advskew: 1 Virtual IP: 192.168.88.44/24 Password: pass123
ifconfig output:
vtnet0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric 0 mtu 1500
description: LAN
options=800b8<VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,LINKSTATE>
ether d2:e4:71:c1:5e:0a
inet6 fe80::d0e4:71ff:fec1:5e0a%vtnet0 prefixlen 64 scopeid 0x1
inet 192.168.88.100 netmask 0xffffff00 broadcast 192.168.88.255
inet 192.168.88.44 netmask 0xffffff00 broadcast 192.168.88.255 vhid 1
carp: MASTER vhid 1 advbase 1 advskew 0
media: Ethernet 10Gbase-T <full-duplex>
status: active
nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
Wireshark:
Frame 1: 70 bytes on wire (560 bits), 70 bytes captured (560 bits)
Ethernet II, Src: IETF-VRRP-VRID_01 (00:00:5e:00:01:01), Dst: IPv4mcast_12 (01:00:5e:00:00:12)
Internet Protocol Version 4, Src: 192.168.88.100, Dst: 224.0.0.18
Common Address Redundancy Protocol
Version 2, Packet type 1 (Advertisement)
Virtual Host ID: 1
Advertisement Skew: 0
Auth Len: 7
Demotion indicator: 0
Adver Int: 1
Checksum: 0xcf0c [correct]
[Checksum Status: Good]
Counter: 15630591288068578258
HMAC: db894a44db44e04954f8bae9401eb4059db6c977