Ciscozine2 is the default gateway for the Vlan 200 (192.168.0.1). On the other end, there is an FTP server (192.168.0.200) which is connected to Ciscozine2 元Switch. The client has the IP address 10.0.0.100 and it is connected to Ciscozine1 元Switch which is the default gateway for the Vlan 100 (10.0.0.1). Suppose to have a client that wants to download a file from a FTP server. How to understand unicast flooding due to asymmetric routing: Remember: In 元 Switches, the default ARP table aging time is 4 hours while the CAM holds the entries for only 5 minutes. Ternary Content Addressable Memory (TCAM) – Not required to understand the unicast flooding behavior.If a MAC address is found already present in the table for the correct arrival port, only its timestamp is updated. If a MAC address learned on one switch port has moved to a different port, the MAC address and timestamp are recorded for the most recent arrival port. The port of arrival and the VLAN are both recorded in the table, along with a timestamp. CAM: As frames arrive on switch ports, the source MAC addresses are learned and recorded in the CAM table.All hosts within the broadcast domain receive the ARP request, and only Host A responds with its MAC address. Host B generates a broadcast message for all hosts within the broadcast domain to obtain the MAC address associated with the IP address of Host A. For example, Host B wants to send information to Host A but does not have the MAC address of Host A in its ARP cache. ARP: Maps an IP address to a MAC address in order to provide IP communication within a Layer 2 broadcast domain.To fully understand this process remember that the 元Switch has three tables: If the return path passes through another firewall, the packet will not be allowed to traverse the firewall from the lower to higher security domain because the firewall in the return path will not have any state information.Īnother problem than can occur is unicast flooding where the cause of flooding is that destination MAC address of the packet is not in the L2 forwarding table of the switch. The firewall will be an exit point from one security domain to the other. For example, in firewalls, state information is built when the packets flow from a higher security domain to a lower security domain. Asymmetric routing is not a problem by itself, but will cause problems when Network Address Translation (NAT) or firewalls are used in the routed path.
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