Siemens SIMATIC NET SCALANCE SC-600 Configuration Manual page 39

ICMP packet type 5 - Redirect
Host A wants to send an IP frame to host C. Host C is not located in the same subnet as
host A. For this reason host A sends the IP frame to its default gateway. The default
gateway of host A is interface 1 of router A. Via its routing table, however, router A
knows that subnet C is reachable via router B. Router B connects subnet A with subnet
C. Router A sends a redirect message to host A. In this, router A instructs host A in
future to send IP frames to host C via router B whose IP address is contained in the
redirect message. The initial IP frame is sent by router A directly to router B that
forwards it to Host C.
Conditions for sending redirect messages
• The IP frame is received and sent via the same interface of router A.
• The source IP address (host A) is from the same subnet as the next hop address
(router B) in the routing table.
• The IP frame is not affected by a source NAT rule (masquerading, source NAT or
NETMAP).
• So that router A forwards the initial IP frame to router B, a firewall rule vlanX → vlanX
is required.
SCALANCE SC-600 Web Based Management (WBM)
Configuration Manual, 10/2021, C79000-G8976-C475-03
Technical basics
3.3 ICMP
39