Selecting Apache's Outgoing Proxy Address
Use ProxySourceAddress for an assigned local source and account for route selection, NAT and address families separately.
For Apache 2.4's outgoing proxy source, use ProxySourceAddress in server configuration:
ProxySourceAddress 192.0.2.20Replace the documentation address with an appropriate assigned source on the host. This neither allocates an address nor changes the listener. Listen and virtual-host configuration govern incoming clients.
The operating system still chooses the route. An address belonging to provider A is not guaranteed to work through provider B's default gateway. A multihomed Linux host may need a compatible source-based routing policy.
Address families matter: an IPv4 source cannot be used as the source of an IPv6 connection. Check which destination family the failing request selected.
Finally, distinguish the local source from the public exit. NAT or a parent proxy may replace it. If Apache bound correctly but the website sees another address, follow the next hop before changing the listener or widening access.