![]() Alias the cluster addresses on the correct interface.Replace $INTERFACE with actual interface name: Loose routing (recommended): sysctl -w .rp_filter=2ĭisabling reverse path filtering (alternative): sysctl -w .rp_filter=0 Disabling the reverse path filtering setting disables source address verification.Īvoid trouble: If collocated servers are defined, define loose routing for the reverse path filtering setting. Loose routing allows responses from any address aliased on the server. The operating system recommends loose routing rather than disabling reverse path filtering. ![]() Modify the reverse path filtering setting to use loose routing (2) or disable reverse path filtering. With strict routing, cluster responses are discarded by the server. The Reverse path filtering setting is enabled for strict routing by default.Modify arp_announce to 2 to prevent addresses on the loopback interface from being announced on the network. Modify the arp_ignore setting to 3 so ARP responses are not generated for host-scoped addresses. Prevent cluster advertisement (ARP suppression).When Load Balancer’s MAC forwarding or encapsulated MAC forwarding is used, the following configuration steps must be taken on each Linux server: Recall that the cluster address must be assigned to the loopback to prevent conflicts with the Load Balancer and the loopback interface cannot transmit packets on the network. The cluster address is not configured on the ethernet interface so responses from the server to the client are discarded. With strict routing, traffic must use an address assigned to the sending interface, otherwise, the traffic is discarded. Servers are configured with a strict routing policy by default. The reverse path filtering setting controls the addresses allowed to send traffic on the network. The default loopback address, 127.0.0.1, is never advertised since it is reserved for the local machine. ARP settings must be modified to prevent loopback address advertisement. The Load Balancer no longer distributes connections for the cluster. If the server advertises the cluster address, the server receives all the cluster traffic. Linux, by default, advertises addresses configured on all interfaces, including the loopback. Responses are routed directly back to the client and do not flow through the Load Balancer. The server transmits responses from an ethernet interface with the cluster address as the source address. Aliasing the cluster IP on the loopback interface allows the server to receive forwarded packets. The servers receive network traffic for any address configured on the server. This address is reserved to represent the local machine. A special address of 127.0.0.1 is always assigned to the loopback interface. The loopback interface is a virtual interface that is always present and cannot transmit data on the network. The loopback interface is a special interface that allows local socket communication. Operating system configuration changes are required for all Linux servers defined to receive MAC-forwarded or encapsulated MAC-forwarded traffic. A common method is to add the sysctl commands to the /etc/nf file.Īfter the configuration changes are made, if the expected behavior is not observed, review your specific operating system manual. Consult your operating system documentation for administering persistent settings. Users with Linux for System z must review this material.Īvoid Trouble: Make the server configuration changes persistent such that changes are retained when the system is rebooted. To configure Linux servers to process MAC or encapsulated MAC forwarded traffic, you must add the cluster address as an alias on the loopback adapter, suppress advertisement of the cluster address, and modify reverse path filtering. The cluster address is added to the tunnel interface. However, if a collocated server is defined, the Load Balancer creates a special tunnel interface named ibmulb. The collocated server and the Load Balancer compete for resources and cause degraded performance and response time. Servers on the same machine as a Load Balancer are called collocated servers. Collocated servers are not recommended. To allow this behavior, the cluster address is added to the loopback device on the back-end servers as shown: When the MAC forwarding method is configured with WebSphere ® Edge Load Balancer, you must ensure that cluster-addressed traffic can be accepted by the stacks of the back-end servers. The Linux™ operating system employs a host-based model of advertising hardware addresses to IP addresses with the Address Resolution Protocol (ARP). This model is incompatible with the back-end server or collocated server requirements for Load Balancer's Media Access Control (MAC) forwarding method. Why is configuring MAC and encapsulated MAC forwarding for WebSphere ® Edge Load Balancer different on Linux™?
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