запустил, попробовал, не воспроизводится
[2015-12-02 22:46:19.686] ipoe0: b12495e228bf9a8f: recv [DHCPv4 Request xid=2c1c0249 ciaddr=192.168.12.2 chaddr=52:54:00:12:34:61 <Message-Type Request> <Host-Name debian-i386> <Request-List Subnet,Broadcast,Time-Offset,Router,Domain-Name,DNS,119,Host-Name,44,47,MTU,Classless-Route,NTP>]
[2015-12-02 22:46:19.686] ipoe0: b12495e228bf9a8f: send [DHCPv4 Ack xid=2c1c0249 ciaddr=192.168.12.2 yiaddr=192.168.12.2 chaddr=52:54:00:12:34:61 <Message-Type Ack> <Server-ID 192.168.12.1> <Lease-Time 60> <T1 60> <Router 192.168.12.1> <Subnet 255.255.255.0>]
[2015-12-02 22:46:29.831] cli: telnet: new connection from 127.0.0.1
[2015-12-02 22:46:34.031] ipoe0: b12495e228bf9a8f: terminate
[2015-12-02 22:47:18.583] ipoe0: b12495e228bf9a8f: recv [DHCPv4 Request xid=2c1c0249 ciaddr=192.168.12.2 chaddr=52:54:00:12:34:61 <Message-Type Request> <Host-Name debian-i386> <Request-List Subnet,Broadcast,Time-Offset,Router,Domain-Name,DNS,119,Host-Name,44,47,MTU,Classless-Route,NTP>]
[2015-12-02 22:47:18.584] send [DHCPv4 Nak xid=2c1c0249 chaddr=52:54:00:12:34:61 <Message-Type Nak>]
[2015-12-02 22:47:18.585] ipoe0: b12495e228bf9a8f: radius(1): req_enter 1
[2015-12-02 22:47:18.586] ipoe0: b12495e228bf9a8f: send [RADIUS(1) Accounting-Request id=3 <User-Name "eth1.2"> <NAS-Identifier "accel-ppp"> <NAS-IP-Address 192.168.11.9> <NAS-Port 15> <NAS-Port-Id "ipoe0"> <NAS-Port-Type Ethernet> <Calling-Station-Id "52:54:00:12:34:61"> <Called-Station-Id "eth1.2"> <Acct-Status-Type Stop> <Acct-Authentic RADIUS> <Acct-Session-Id "b12495e228bf9a8f"> <Acct-Session-Time 83> <Acct-Input-Octets 656> <Acct-Output-Octets 1128> <Acct-Input-Packets 2> <Acct-Output-Packets 6> <Acct-Input-Gigawords 0> <Acct-Output-Gigawords 0> <Framed-IP-Address 192.168.12.2> <Acct-Terminate-Cause NAS-Request>]
[2015-12-02 22:47:18.586] ipoe0: b12495e228bf9a8f: pppd_compat: ip-down started (pid 9666)
[2015-12-02 22:47:18.588] ipoe0: b12495e228bf9a8f: pppd_compat: ip-down finished (1)
[2015-12-02 22:47:18.589] ipoe0: b12495e228bf9a8f: radius(1): req_exit 0
[2015-12-02 22:47:18.589] ipoe0: b12495e228bf9a8f: ipoe: session finished
[2015-12-02 22:47:18.596] recv [RADIUS(1) Accounting-Response id=3]
[2015-12-02 22:47:28.079] : : recv [DHCPv4 Discover xid=2f25873 chaddr=52:54:00:12:34:61 <Message-Type Discover> <Host-Name debian-i386> <Request-List Subnet,Broadcast,Time-Offset,Router,Domain-Name,DNS,119,Host-Name,44,47,MTU,Classless-Route,NTP>]
у тебя в ip-down видимо что-то происходит не обычное