Setup CARP unicast peer,
```lang=sh
#!/bin/sh
kldload -n carp
ifconfig epair create
jail -ic name=foo vnet persist
jail -ic name=bar vnet persist
ifconfig epair0b vnet bar
ifconfig epair0a vnet foo
ifconfig -j foo epair0a inet 192.168.2.224/24
ifconfig -j foo epair0a vhid 1 peer 192.168.2.1 192.168.2.99/32 alias
ifconfig -j bar epair0b inet 192.168.2.1/24
ifconfig -j bar epair0b vhid 1 peer 192.168.2.224 192.168.2.99/32 alias
```
Make epair0a in jail foo a CARP backup, and observe the traffic in jail bar,
```
# ifconfig -j foo epair0a vhid 1 state backup
# ifconfig -j foo epair0a
epair0a: flags=1008943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST,LOWER_UP> metric 0 mtu 1500
options=8<VLAN_MTU>
ether 02:02:cc:b9:51:0a
inet 192.168.2.224 netmask 0xffffff00 broadcast 192.168.2.255
inet 192.168.2.99 netmask 0xffffffff broadcast 192.168.2.99 vhid 1
groups: epair
carp: BACKUP vhid 1 advbase 1 advskew 0
peer 224.0.0.18 peer6 ff02::12
media: Ethernet 10Gbase-T (10Gbase-T <full-duplex>)
status: active
nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
# ifconfig -j bar epair0b
epair0b: flags=1008943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST,LOWER_UP> metric 0 mtu 1500
options=8<VLAN_MTU>
ether 02:02:cc:b9:51:0b
inet 192.168.2.1 netmask 0xffffff00 broadcast 192.168.2.255
inet 192.168.2.99 netmask 0xffffffff broadcast 192.168.2.99 vhid 1
groups: epair
carp: MASTER vhid 1 advbase 1 advskew 0
peer 192.168.2.224 peer6 ff02::12
media: Ethernet 10Gbase-T (10Gbase-T <full-duplex>)
status: active
nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>
# jexec bar tcpdump -enpi epair0b -T carp -c 3
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on epair0b, link-type EN10MB (Ethernet), snapshot length 262144 bytes
15:06:35.769990 02:02:cc:b9:51:0b > 02:02:cc:b9:51:0a, ethertype IPv4 (0x0800), length 70: 192.168.2.1 > 192.168.2.224: CARPv2-advertise 36: vhid=1 advbase=1 advskew=0 authlen=7 counter=10996631475009634537
15:06:36.831949 02:02:cc:b9:51:0b > 02:02:cc:b9:51:0a, ethertype IPv4 (0x0800), length 70: 192.168.2.1 > 192.168.2.224: CARPv2-advertise 36: vhid=1 advbase=1 advskew=0 authlen=7 counter=10996631475009634538
15:06:37.870947 02:02:cc:b9:51:0b > 02:02:cc:b9:51:0a, ethertype IPv4 (0x0800), length 70: 192.168.2.1 > 192.168.2.224: CARPv2-advertise 36: vhid=1 advbase=1 advskew=0 authlen=7 counter=10996631475009634539
```