L2 SECURITY

• Violation modes of port-security
  • Shutdown
    • send port to err-disable
  • Protect
    • Violators cannot send traffic in , no alert is raised
  • Restrict
    • Violators cannot send traffic in
    • Generates SNMP/ Syslog
  • HSRP uses 2 MAC addresses ( NOTE )
  • During configuration, check if some traffic might inadvertantly trigger this port-security feature.
• 2 ways to recover a port from err-disable
  • err-disable recovery configured
  • shut/no-shut
• We can also configure a static ” Null route” a MAC address
• When we block multicast, then some unicast/broadcast traffic also gets blocked in Storm-control ( read more on this )
• “switchport protected” -> Mini PVLAN like configuration
• When configuring VLAN Maps, ensure that ARP traffic is allowed ( most of the time, this is needed )
• PVLAN requires Transparent ( VTP ) mode configuration on the switch

ATTACK MITIGATION

• VLAN HOPPING ATTACK
  • 2 variations
    • Hosts runs DTP to form a trunk with the adjacent switch
    • Host sends frames double tagged with 802.1q
  • Mitigation
    • Ensure that all host-facing ports are statically assigned as access ports (switchport mode access )
    • Don’t ever use VLAN 1 as the default VLAN
• CAM TABLE ATTACKS
  • port-security -> Mitigation
  • Shutting down the port is the best option
• DHCP STARVATION ATTACKS
  • Tons of DHCP requests exhaust the DHCP pool.
  • Victim hosts are starved of a DHCP lease.
  • Could be a DOS/ MITM attack
  • Mitigation
    • DHCP Snooping
    • Ensure that all switches running a the particular VLAN have DHCP snooping turned on ( talk to the proctor )
• ROGUE DHCP SERVER ATTACK
  • Mitigation : DHCP Snooping ( trust )
    • Can also use Port ACLs/VACLs
    • We can also use the “ip dhcp snooping Limit” command to limit the flood.
• ARP SPOOFING
  • Gratuitous ARP -> Send ARP replies regularly without valid requests ( to refresh the ARP caches of the devices )
  • This can be a good playground to lauch MITM attacks
  • Mitigation
    • DHCP snooping with DAI
    • or ARP acls with DAI ( for static IP addressing )
    • If switches don’t support snooping or ARP inspection
      • IP ARP uses ethertype 0×806
      • IP uses Ethertype 0×800
      • This can be used to block the ARP traffic
    • Bad configuration of this can cause problems later ( reload, reboot ,etc ) . So remember, it won’t immediately show up due to ARP caching on the devices
• MAC SPOOFING
  • Mitigation
    • IP Source guard
      • Consults the DHCP Snooping table
    • We can also use port-security
• IP SPOOFING
  • Mitigation
    • RFC 1918/2827/3330 BOGON ingress filtering
    • uRPF
  • RFC 2827 is bidirectional
    • Traffic leaving should have the internal address
    • Traffic entering from the outside, should not have the internal address
  • uRPF takes into consideration all equal cost paths(urpf accepts both the paths as the reverse path ) into consideration when determining the interface upon which a packet should be received on . It even understands EIGRP unequal cost load-balancing.
• SMURF/FRAGGLE ATTACK
  • Mitigation -> no ip directed broadcast
    • uRPF also does the job
    • via CAR/MQC
    • via Blackholing ( either source/destination based )

STANDARD BLACKHOLE FILTERING

• Problem is legit traffic to the destination also gets blocked
• Matches only by destination
• Ensure that the “no ip unreachables” is configured on the Edge -routers

SOURCE-BASED BLACKHOLE FILTERING

• There is a uRPF statement on the EDGE router
• The trigger will be a route for the “source IP”s next hop ( instead of the destination IP , like the previous configuration )
• If we do not add a “deny” route-map after the first route-map, any other static routes will get redistributed into the BGP.

SYN FLOODING

• Mitigation
  • TCP Intercept
  • IOS CBAC/ ZBF
  • PIX/ASA MPF connection limits
  • SYN policing with CAR/MQC

Network scanning can be blocked by using ASA Threat detections, IPS/IDS , etc

• To drop ip options you can use the global config command : “ip options drop”, or we can drop using ACL’s ” access-list 101 deny ip any any option.”

I’m now officially done with the bootcamp. I would recommend this to everyone , when they are almost done with their Vol 1 labs. There was a big section in Day 5 about Strategies and tips to be followed during the lab and that was very insightful and i thoroughly enjoyed it

To be honest, i don’t know what exactly i wanna do for the next couple of days/ weeks. I’m stuck between Vol 2 labs (or) Go through the CCIE-sec blueprint and configure each and every item in detail and also make a list of the Doc-CD references for each.

I’ll definitely have an answer soon .

I’m really lucky to have found an awesome support community online who continue to inspire/motivate/support me. Paul Stewart , Brian Almond and Ryan Schuett are some people i look up to someday i want to know as much as these dudes

Cheers,

TacACK