I currently have ipv4.ip_forward enabled to route packets between multiple interfaces.I am now scaling up the system to 8 interfaces, but I want to limit the routing between interfaces/addresses.One option is to use the firewalld, but I'm deploying this on an older version of RH so it would be done via iptables. 
Limiting IP forwarding between certain interfaces/networks
linux;iptables;forwarding
Actually iptables is suited very well to restrict this. The filter table, where packets are allowed or blocked has three chains. In each chain rules can be defined to match packets and trigger an action if a packet is matched. Against which chain of rules a packet is matched depends on the direction of the packet relative to the host where iptables is running:INPUT: Incoming packet destined for the local hostOUTPUT: Outgoing packets originating from the local hostFORWARD: Packets destined for another host and need to be forwardedNow for example if a packet is to be forwarded and has no rule that matches it in the FORWARD chain, it will be handled according to the policy set on this chain, which is by default: ACCEPT. The packet will be allowed to pass. This command will show the policies and rules if any of them are defined:iptables -t filter -vnLThe table is specified using -t <table>, filter is the default table if none is specified, so the following command is equivalent:iptables -vnLTo block all packets for forwarding, the policy on this chain can be set to REJECT or DROP as followsiptables -P FORWARD REJECTNow all packets which are to be forwarded are rejected if no rule in the FORWARD chain explicitly accepts them.For internal traffic, you likely want a REJECT policy.  This will notify clients immediately that the path is closed.  You may want DROP rules for traffic originating from an external network.To explicitly allow certain packets to pass, rules are appended to those chains, which are matched aigainst packets in the order those rules were defined. For example to allow all traffic coming in on eth0 and based on the routing to be forwarded to eth1:iptables -A FORWARD -i eth0 -o eth1 -j ACCEPTAnd for example to only allow packets from the 10.0.0.0/24 subnet to pass in the opposite direction:iptables -A FORWARD -i eth1 -o eth0 -s 10.0.0.0/24 -j ACCEPTFor a detailed description of all the parameters refer to the iptables manpage and the iptables-extensions manpage.