metrotek Bercut-ET, Operation Manual

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5.9 Loopback 45
5.9 Loopback
The Loopback function is necessary for networks testing in compliance
with the RFC 2544, as well as for a number of other tasks. This function
allows to test the network without changing it’s settings. Network testing
with the Loopback function can be performed at the following OSI layers:
•
at the Physical layer (L1) all the incoming traffic is being retransmit-
ted backward without changing; statistics is gathered for the incoming
traffic;
• at the Data link layer (L2) , all the incoming frames are being retrans-
mitted backward with swapping destination and source MAC addresses
or without swapping MAC addresses.
Bercut-ET supports substitu-
tion of destination and/or source MAC address with user-defined MAC
address. Both incoming and outgoing traffic statistics are gathered.
Note:
for the loopback at the L2 or L3 layers, packets with identical
destination and source MAC addresses as well as OAM protocol data units
(OAMPDU) and ARP-requests, are not being retransmitted.
•
At the Network layer (L3) all incoming packets are being retrans-
mitted backward with source and destination IP addresses swapping.
Bercut-ET supports substitution of destination and/or source IP ad-
dress with user-defined IP address. Both incoming and outgoing traffic
statistics are being gathered.
Note:
if the incoming packet contains the label, it will be retransmitted
without changing it’s value.
• At the Transport layer (L4) all incoming packets are being retrans-
mitted backward (without error packets) with source and destination IP
addresses and source and destination TCP/UDP port numbers swap-
ping.
Note: if the incoming packet contains the label, it will be retransmitted
without changing it’s value.
Bercut-ET. Operations manual