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HP Switch 7750 - Does not drop traffic when a null route is configured
3Com Knowledgebase Article
HP Switch 7750 - does not drop traffic when a null route is configured
All current software for all types of fabric
0231A43G - S7500 Fabric 768G
0235A13T - S7506 Chassis w/2 AC PSU & Fan
0235A13X - S7506R Chassis + 2 AC PS
0235A13Y - S7506R Chassis + 2 DC PS
0235A14B - S7502 Chassis
0235A14T - S7503 Chassis
0231A43H - S7500 96Gbps Salience III SRPU
0231A43F - S7500 Fabric 384G 4 SFP
3C16894 - Switch 7754 4-slot Chassis Kit w/out Fabric
3C16895 - Switch 7757 7-slot Chassis Kit w/out Fabric
3C16896 - Switch 7758 8-slot Redundant AC Chassis Kit
3C16886 - Switch 7750 96Gig Switch Fabric for all Chassis
3CR1686593-V3.3 - Switch 7750 Advanced Feature Software Version 3.3 for 96Gbps Switch Fabric
3CR16870093-301 - Switch 7700 Advanced Feature Software Version 301.51 for 32/64Gbps Switch Fabrics
Instead of having a static route for 18.104.22.168/32, it is suggested to have the following static arp entry configured:
arp static 22.214.171.124 0011-2222-3333 20 g 2/0/1
Once this line is configured, the return traffic to 126.96.36.199 will be delivered to G2/0/1 with MAC address of 0011-2222-3333, which the PC will not respond to.
SW7750 - does not drop traffic when null route is configured.
The following configuration is on the SW7750:
ip address 188.8.131.52 255.255.255.0
ip route-static 184.108.40.206 255.255.255.255 NULL 0 preference 60
The purpose of the Null 0 ip route configuration is to prevent the PC with IP address 220.127.116.11 to communicate with any devices outside of the subnet. However when the static route is applied to the SW7750, it is seen that the 18.104.22.168/32 was still able to communicate with devices outside of local subnet.
When dealing with the local subnet the SW7750 does not use the routing table for routing, instead the arp table, which has the port information and MAC address information for 22.214.171.124/32 - the routing table is not indeed used for local subnet.
In this case, since the arp table has the 126.96.36.199 entry already, the routing table is bypassed - traffic is delivered to 188.8.131.52/32 directly from arp table lookup.