On your proxmox server edit /etc/interfaces and add a vmbr1 interface like so
auto lo
iface lo inet loopback
auto vmbr0
iface vmbr0 inet static
address 167.114.101.88
netmask 255.255.255.0
gateway 167.114.101.254
broadcast 167.114.101.255
network 167.114.101.0
bridge_ports eth0
bridge_stp off
bridge_fd 0
# Internal Network
auto vmbr1
iface vmbr1 inet static
address 10.0.1.1/23
bridge_ports dummy0
bridge_stp off
bridge_fd 0
post-up /sbin/iptables -t nat -A POSTROUTING -o vmbr0 -j MASQUERADE
pre-down /sbin/iptables -t nat -D POSTROUTING -o vmbr0 -j MASQUERADE
Bring up the new vmbr1 interface
ifdown vmbr1 && ifup vmbr1
Then enable ip forwarding in /etc/sysctl.conf
net.ipv4.ip_forward=1
Load the new values
sysctl -p /etc/sysctl.conf
On your vm configure networking like so
auto eth0
iface eth0 inet static
address 10.0.1.100
netmask 255.255.254.0
gateway 10.0.1.1