# Advanced Switching Topics

IP source guard without DHCP When DHCP snooping is enabled, a switch maintains a database of the DHCP addresses assigned to the hosts connected to each access port. IP source guard references this database when a packet is received on any of these interfaces and compares the source address to the assigned address listed in the database. If the source address differs from the "allowed" address, the packet is assumed to spoofed and is discarded. Assuming DHCP isn't available or in use on a subnet, static IP bindings can be manually configured per access port to achieve the same effect.
Configuration
sw1(config)#ip dhcp snooping
sw1(config)#ip dhcp snooping vlan 146
sw1(config)#interface FastEthernet0/13
switchport access vlan 146
switchport trunk encapsulation dot1q
switchport mode access
ip verify source
sw1(config)#interface FastEthernet0/16
switchport access vlan 146
switchport mode access
ip verify source
sw1(config)#ip source binding 000D.29C0.F180 vlan 146 155.1.0.2 interface Fa0/13
sw1(config)#ip source binding 000D.29E3.AB00 vlan 146 155.1.0.3 interface Fa0/16
sw1(config)#do sh ip source binding
MacAddress IpAddress Lease(sec) Type VLAN Interface
0:0D:29:C0:F1:80 155.1.0.2 infinite static 146 FastEthernet0/13
00:0D:29:E3:AB:00 155.1.0.3 infinite static 146 FastEthernet0/16
Total number of bindings: 2
sw1(config)#do sh ip verify source
Interface Filter-type Filter-mode IP-address Mac-address Vlan
Fa0/13 ip active 155.1.0.2 146
Fa0/16 ip active 155.1.0.3 146
sw1(config)#
If you don't enable the dhcp snooping on sw1 it will show the following under Filter-
mode lists inactive-no-snooping-vlan for any
sw1(config)#no ip dhcp snooping vlan 146
sw1(config)#do sh ip verify source
Interface Filter-type Filter-mode IP-address Mac-address Vlan
Fa0/13 ip inactive-no-snooping-vlan
Fa0/16 ip inactive-no-snooping-vlan change the ip address of sw2 to 155.1.0.22 now try to ping 155.1.0.3 (sw3 ip address) the following error messages will be generated in sw1(3560).
sw1(config)#
02:30:26: %SW_DAI-4-DHCP_SNOOPING_DENY: 1 Invalid ARPs (Req) on Fa0/13, vlan 146.([000d.29c0.
f180/155.1.0.22/000d.29e3.ab00/155.1.0.3/02:30:25 UTC Mon Mar 1 1993]) 02:30:26: %SW_DAI-4-DHCP_SNOOPING_DENY: 1 Invalid ARPs (Res) on Fa0/13, vlan 146.([000d.29c0.
f180/155.1.0.22/ffff.ffff.ffff/155.1.0.22/02:30:25 UTC Mon Mar 1 1993])
02:30:33: %SW_DAI-4-DHCP_SNOOPING_DENY: 1 Invalid ARPs (Req) on Fa0/13, vlan 146.([000d.29c0. f180/155.1.0.22/0000.0000.0000/155.1.0.3/02:30:32 UTC Mon Mar 1 1993])
02:30:35: %SW_DAI-4-DHCP_SNOOPING_DENY: 1 Invalid ARPs (Req) on Fa0/13, vlan 146.([000d.29c0
f180/155.1.0.22/0000.0000.0000/155.1.0.3/02:30:34 UTC Mon Mar 1 1993]) 02:30:37: %SW_DAI-4-DHCP_SNOOPING_DENY: 1 Invalid ARPs (Req) on Fa0/13, vlan 146.([000d.29c0.
f180/155.1.0.22/0000.0000.0000/155.1.0.3/02:30:36 UTC Mon Mar 1 1993])
02:30:39: %SW_DAI-4-DHCP_SNOOPING_DENY: 1 Invalid ARPs (Req) on Fa0/13, vlan 146.([000d.29c0. f180/155.1.0.22/0000.0000.0000/155.1.0.3/02:30:38 UTC Mon Mar 1 1993])
02:30:40: %SW_DAI-4-DHCP_SNOOPING_DENY: 1 Invalid ARPs (Req) on Fa0/13, vlan 146.([000d.29c0.
f180/155.1.0.22/0000.0000.0000/155.1.0.3/02:30:40 UTC Mon Mar 1 1993])
02:30:42: %SW_DAI-4-DHCP_SNOOPING_DENY: 1 Invalid ARPs (Req) on Fa0/13, vlan 146.([000d.29c0.
f180/155.1.0.22/0000.0000.0000/155.1.0.3/02:30:42 UTC Mon Mar 1 1993])
02:30:44: %SW_DAI-4-DHCP_SNOOPING_DENY: 1 Invalid ARPs (Req) on Fa0/13, vlan 146.([000d.29c0.
f180/155.1.0.22/0000.0000.0000/155.1.0.3/02:30:44 UTC Mon Mar 1 1993])
02:30:46: %SW_DAI-4-DHCP_SNOOPING_DENY: 1 Invalid ARPs (Req) on Fa0/13, vlan 146.([000d.29c0.
f180/155.1.0.22/0000.0000.0000/155.1.0.3/02:30:46 UTC Mon Mar 1 1993])
sw1(config)# 02:39:44: %SW_DAI-4-DHCP_SNOOPING_DENY: 1 Invalid ARPs (Req) on Fa0/13, vlan 146.([000d.29c0.
f180/155.1.0.22/000d.29e3.ab00/155.1.0.3/02:39:43 UTC Mon Mar 1 1993])
02:39:44: %SW_DAI-4-DHCP_SNOOPING_DENY: 1 Invalid ARPs (Res) on Fa0/13, vlan 146.([000d.29c0.
f180/155.1.0.22/ffff.ffff.ffff/155.1.0.22/02:39:43 UTC Mon Mar 1 1993]) sw1(config)# do sh ip arp inspection Source Mac Validation : Disabled Destination Mac Validation : Disabled IP Address Validation : Disabled
146 Enabled Active
Vlan ACL Logging DHCP Logging
sw1(config)#ip arp inspection vlan 146
DAI ON NON DHCP SERVER ON SW1 sw1(config)#ip arp inspection vlan 146
sw1(config)#ip arp inspection filter vlan146 vlan 146
sw1(config)#interface FastEthernet0/13
switchport access vlan 146
switchport trunk encapsulation dot1q
switchport mode access
ip arp inspection limit rate 50 burst interval 10
sw1(config)#interface FastEthernet0/16
switchport access vlan 146
switchport mode access
sw1(config)#interface FastEthernet0/19
switchport access vlan 146
switchport mode access
sw1(config)#arp access-list vlan146
permit ip host 155.1.0.2 mac host 000d.29c0.f180
permit ip host 155.1.0.3 mac host 000d.29e3.ab00
ON SW2
sw2(config)#interface FastEthernet0/13
no switchport
ip address 155.1.0.2 255.255.255.0
no shutdown
ON SW3
sw3(config)#interface FastEthernet0/13
no switchport
ip address 155.1.0.3 255.255.255.0
no shutdown
ON SW4
interface FastEthernet0/13
no switchport
ip address 155.1.0.4 255.255.255.0
no shutdown
when you try to ping from sw4 it will generate arp error in sw1 but there will be no issue in case of sw2 and sw3 as the ip address to mac-address mapping is done by using arp-acl.