Reflective Relay and Loopback Suppression

Reflective relay allows the packet from a device to be returned back from the same downstream port that delivered the packets. The most common use case is when the same interface is used to transmit and receive packets. This can be seen while using Virtual Ethernet Packet Aggregation (VEPA).

In the Virtual Ethernet Bridging (VEB) model, the hypervisor has a virtual switch or vswitch which acts as Layer2 switch in software. This allows intra-VM communication in software and packets do not have to leave the server. This requires a highly complex and expensive server and accounts for high overhead to accomplish network processing.

VEPA can be installed on the server to aggregate virtyal machine packets and pass them to the physical switch. The physical switch thus offloads the switching activities from the servers vswitch.

When aggregated packets are received on the switch, reflective relay and disabling loopback suppression must be configured on the switch, as some of the packets may have to be sent back to the same server, destined to another virtual machine residing on the same server. This will return those packets to the original device using the same port that delivered the packet to the switch.

24.1 VLAN Commands for Reflective Relay

SEFOS# show vlan
 
Vlan database
-------------
Vlan ID             : 1
Member Ports        : Ex0/1, Ex0/2, Ex0/3, Ex0/4, Ex0/5, Ex0/6
                      Ex0/13, Ex0/14, Ex0/15, Ex0/16, Ex0/17, Ex0/18
                      Ex0/19, Ex0/20, Ex0/21, Ex0/22, Ex0/23, Ex0/24
Untagged Ports      : Ex0/1, Ex0/2, Ex0/3, Ex0/4, Ex0/5, Ex0/6
                      Ex0/7, Ex0/8, Ex0/9, Ex0/10, Ex0/11, Ex0/12
                      Ex0/13, Ex0/14, Ex0/15, Ex0/16, Ex0/17, Ex0/18
                      Ex0/19, Ex0/20, Ex0/21, Ex0/22, Ex0/23, Ex0/24
Forbidden Ports     : None
Reflective-Relay    : Disabled
Name                :
Status              : Other

SEFOS# c t
SEFOS(config)# vlan 100
SEFOS(config-vlan)# vlan active
SEFOS(config-vlan)# ports add extreme-ethernet 0/21
SEFOS(config-vlan)# set reflective-relay enable
SEFOS(config-vlan)# end
SEFOS# 
SEFOS# show vlan
 
Vlan database
-------------
Vlan ID             : 1
Member Ports        : Ex0/1, Ex0/2, Ex0/3, Ex0/4, Ex0/5, Ex0/6
                      Ex0/7, Ex0/8, Ex0/9, Ex0/10, Ex0/11, Ex0/12
                      Ex0/13, Ex0/14, Ex0/15, Ex0/16, Ex0/17, Ex0/18
                      Ex0/19, Ex0/20, Ex0/21, Ex0/22, Ex0/23, Ex0/24
Untagged Ports      : Ex0/1, Ex0/2, Ex0/3, Ex0/4, Ex0/5, Ex0/6
                      Ex0/7, Ex0/8, Ex0/9, Ex0/10, Ex0/11, Ex0/12
                      Ex0/13, Ex0/14, Ex0/15, Ex0/16, Ex0/17, Ex0/18
                      Ex0/19, Ex0/20, Ex0/21, Ex0/22, Ex0/23, Ex0/24
Forbidden Ports     : None
Reflective-Relay    : Disabled
Name                :
Status              : Other
----------------------------------------------------
Vlan ID             : 100
Member Ports        : Ex 0/21
Untagged Ports      : None
Forbidden Ports     : None
Reflective-Relay    : Enabled
Name                :
Status              : Other

24.2 Interface Commands for Loopback Suppression

SEFOS(config)# interface extreme-ethernet 0/21
SEFOS(config-if)# set loopback-suppress disable
SEFOS(config-if)# end
SEFOS# 
SEFOS# show interface extreme-ethernet 0/21
 
Ex0/21 up, line protocol is up (connected)
Bridge Port Type: Customer Bridge Port
 
Hardware Address is 00:10:e0:1e:20:25
MTU  9216 bytes, Full duplex, 10 Gbps,  No-Negotiation
HOL Block Prevention enabled.
Input flow-control is off,output flow-control is on
 
Link Up/Down Trap is enabled
 
Loopback Suppression is disabled
 
Reception Counters
   Octets                    : 53011
   Unicast Packets           : 0
   Discarded Packets         : 120
   Error Packets             : 0
   Unknown Protocol          : 0
   CRC Errors                : 0
   Symbol Errors             : 0
   Good CRC Frame Size Errors: 0
   Oversized w/ Bad CRC      : 0
 
Transmission Counters
   Octets                    : 72031
   Unicast Packets           : 0
   Discarded Packets         : 0
   Error Packets             : 0
   Bad CRC                   : 0
   Error Drops               : 0
   Timeout Drops             : 0