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Cisco ASA IPS IP fragment missing Alert

Oleg Volkov
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Dear Sirs!


I have two Cisco ASA5515X, and IPSec tunnel between them.
At the inside nets, I have Cisco 3925 and this routers connected together by ipip Tunnel w/o encryption (encrypt traffic made by ASA (IPIP tunnel in the IPSEc tunnel).
This tunnel need for work EIGRP.

====================================
Tunnel interface on router1:

interface Tunnel2
 description -= Tunnel QinQ =-
 bandwidth 100000
 ip address 10.255.0.5 255.255.255.252
 ip mtu 1400
 ip tcp adjust-mss 1360
 tunnel source 10.255.0.67
 tunnel mode ipip
 tunnel destination 10.255.0.68
 service-policy output AGG_POL_TUN1
end

  Policy Map AGG_POL_TUN1
    Class class-default
      Average Rate Traffic Shaping
      cir 100000000 (bps)
      service-policy POL_TUN1


  Policy Map POL_TUN1
    Class EIGRP_CL
      priority 1 (%)
    Class AVAYA
      priority 5 (%)
    Class SERVERS_TO_SERVERS_CL
      bandwidth remaining 60 (%)
      fair-queue
    Class class-default
      bandwidth remaining 40 (%)
      fair-queue

Tunnel interface on the router 2:

interface Tunnel2
 description -= Tunnel QinQ =-
 bandwidth 100000
 ip address 10.255.0.6 255.255.255.252
 ip access-group TUNACL_USERS out
 ip mtu 1400
 ip tcp adjust-mss 1360
 tunnel source 10.255.0.68
 tunnel mode ipip
 tunnel destination 10.255.0.67
 service-policy output AGG_POL_TUN1
end

  Policy Map AGG_POL_TUN1
    Class class-default
      Average Rate Traffic Shaping
      cir 100000000 (bps)
      service-policy POL_TUN1

Policy Map POL_TUN1
    Class AVAYA
      priority 5 (%)
    Class SERVERS_TO_SERVERS_CL
      bandwidth remaining 60 (%)
      fair-queue
    Class EIGRP_CL
      priority 1 (%)
    Class CL_RUTOLL_DISP_NORTH
     police rate 25000000 bps burst 8500000 bytes
       conform-action transmit
       exceed-action drop
    Class class-default
      bandwidth remaining 40 (%)
      service-policy INDEFAULT_MAP

 

ping 10.255.0.6 df-bit size 1400
Type escape sequence to abort.
Sending 5, 1400-byte ICMP Echos to 10.255.0.6, timeout is 2 seconds:
Packet sent with the DF bit set
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms
ping 10.255.0.6 df-bit size 1401
Type escape sequence to abort.
Sending 5, 1401-byte ICMP Echos to 10.255.0.6, timeout is 2 seconds:
Packet sent with the DF bit set
.....
Success rate is 0 percent (0/5)

 

ping 10.255.0.68 source 10.255.0.67 df-bit size 1446
Type escape sequence to abort.
Sending 5, 1446-byte ICMP Echos to 10.255.0.68, timeout is 2 seconds:
Packet sent with a source address of 10.255.0.67
Packet sent with the DF bit set
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms
ping 10.255.0.68 source 10.255.0.67 df-bit size 1447
Type escape sequence to abort.
Sending 5, 1447-byte ICMP Echos to 10.255.0.68, timeout is 2 seconds:
Packet sent with a source address of 10.255.0.67
Packet sent with the DF bit set
M.M.M

====================================

From other router, I ping throught  Tunnel

ping 10.50.2.251 source 10.0.2.1 df-bit size 1400

Type escape sequence to abort.
Sending 5, 1400-byte ICMP Echos to 10.50.2.251, timeout is 2 seconds:
Packet sent with a source address of 10.0.2.1
Packet sent with the DF bit set
!!!!!

ping 10.50.2.251 source 10.0.2.1 df-bit size 1401

Type escape sequence to abort.
Sending 5, 1401-byte ICMP Echos to 10.50.2.251, timeout is 2 seconds:
Packet sent with a source address of 10.0.2.1
Packet sent with the DF bit set
M.M.M
Success rate is 0 percent (0/5)

 

But at the IDS on ASA, I see many alerts (W/O tunnel traffic, I was not see this alert):

 

evIdsAlert: eventId=6820745803980  vendor=Cisco  severity=informational  
  originator:   
    hostId: sensor_south1  
    appName: sensorApp  
    appInstanceId: 1260  
  time: апр 15, 2015 10:42:38 UTC  offset=3  timeZone=MSK  
  signature:   description=IP Fragment Missing Initial Fragment  id=1204  version=S212  type=anomaly  created=20050304  
    subsigId: 0  
    sigDetails: IP Datagram Missing Initial Fragment  
  interfaceGroup: vs0  
  vlan: 0  
  participants:   
    attacker:   
      addr: 0.0.0.0  locality=OUT  
    target:   
      addr: 0.0.0.0  locality=OUT  
      os:   idSource=unknown  type=unknown  relevance=unknown  
  summary: 45  final=true  initialAlert=6820745803978  summaryType=Regular  
  alertDetails: Regular Summary: 45 events this interval ;  
  riskRatingValue: 25  targetValueRating=medium  
  threatRatingValue: 25  
  interface: po0_0  
  protocol: IP protocol 0  

=======================================================

Also, policy-map work, but not good - sometimes, I have loss packet in the class - AVAYA, but traffic, in this class, very small ( < 1 Mbps).

 

What can I do with this?

Thanks!

 

 

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1 Reply 1

Oleg Volkov
Spotlight
Spotlight

Hmm....

It may be L3TPv3:

evIdsAlert: eventId=6820745809096  vendor=Cisco  severity=high  alarmTraits=32768  
  originator:   
    hostId: sensor_south1  
    appName: sensorApp  
    appInstanceId: 1260  
  time: апр 15, 2015 15:41:55 UTC  offset=3  timeZone=MSK  
  signature:   description=IP Fragment Overwrite - Data is Overwritten  id=1203  version=S212  type=anomaly  created=20030801  
    subsigId: 0  
    sigDetails: IP Fragment Overwrite - Data overwritten  
  interfaceGroup: vs0  
  vlan: 0  
  participants:   
    attacker:   
      addr: 10.255.0.74  locality=OUT  
    target:   
      addr: 10.255.0.73  locality=OUT  
      os:   idSource=unknown  type=unknown  relevance=relevant  
  actions:   
    denyPacketRequestedNotPerformed: true  
  alertDetails: InterfaceAttributes:  context="single_vf" physical="Unknown" backplane="PortChannel0/0" ;  
  riskRatingValue: 100  targetValueRating=medium  attackRelevanceRating=relevant  
  threatRatingValue: 100  
  interface: PortChannel0/0  context=single_vf  physical=Unknown  backplane=PortChannel0/0  
  protocol: IP protocol 115  

 

My interface:

interface GigabitEthernet0/0
 description "L2TPV3"
 no ip address
 no ip redirects
 no ip unreachables
 no ip proxy-arp
 ip mtu 1400
 ip tcp adjust-mss 1360
 duplex full
 speed 1000
 no cdp enable
 no mop enabled
 xconnect 10.255.0.73 550 encapsulation l2tpv3 pw-class L2TPV3_Class
end

 

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