# Networking # Backplane Separation Network Segmentation: CVM/host backplane and service traffic vom Management-Netz trennen, plus die IP-Pools, die dabei eine Rolle spielen. # Backplane Network Segmentation #### What it is By default all Controller VM (CVM) traffic shares one interface (CVM eth0): management (Prism, SSH, Rsyslog, SNMP, PE↔PC) and CVM↔CVM cluster-service traffic (Stargate, Cassandra, Zookeeper, Curator) all go out the same NIC and VLAN. **Network Segmentation** moves specific traffic types onto their own dedicated vNIC and VLAN, physically and logically separated from the management network. #### Traffic types you can segment - **Management** (default, eth0) — Prism, SSH, Rsyslog, SNMP, PE↔PC. Anything that needs the default gateway. - **Backplane** (eth2) — CVM↔CVM, Host↔Host and Host↔CVM cluster-service traffic. Always an isolated, **non-routable** VLAN/subnet, kept separate from every other network in use. - **Service** — an AOS feature you choose to move onto its own network, e.g. **Volumes** (iSCSI data services) or **DR/replication** (Cerebro). Unlike Backplane, this network is usually routable — DR traffic has to reach a remote cluster. - **RDMA** — Stargate-only, uses physical NIC passthrough instead of a vNIC. Separate topic from the three above. #### Prerequisites - At least one spare physical NIC per node beyond what the management virtual switch (`vs0`/`br0`) already uses — backplane traffic needs its own uplinks, not a VLAN trunked over the management NICs. - A second virtual switch (e.g. `vs1`/`br1`) built from those spare NICs, present on every node in the cluster. - CVM and AHV host management interfaces (eth0) must stay on the same subnet/VLAN as each other — segmentation only ever pulls extra traffic off eth0, it never changes the management network itself. - All hosts reachable and able to enter maintenance mode one at a time — segmentation is applied per host with a rolling CVM restart. #### Enabling it (Prism Element) Settings (gear icon) → Network Configuration → Internal Interfaces → "Backplane LAN" → Configure. - VLAN ID — a VLAN not used anywhere else on the network. - Subnet + gateway — Backplane itself never routes anywhere, but the wizard still wants a subnet/mask. - Virtual switch to bind it to (`vs1` from the prerequisites above). - IP address pool for the interface — see the *IP Pools* page in this chapter. Prism assigns one address per CVM (and per host, on current AOS) out of this range automatically. Put hosts into maintenance mode one at a time before configuring, exit again once each CVM has restarted onto the new interface: ```bash acli host.enter_maintenance_mode # ... configure/verify backplane on this host ... acli host.exit_maintenance_mode ``` #### Multiple clusters / Prism Central For Service (DR) segmentation spanning a replication pair, Prism Central's Network Segmentation workflow can push the same VLAN/subnet config to several clusters at once — useful to keep both sides of the pair consistent. # IP Pools #### Two different "IP pools" — don't mix them up Nutanix reuses the term "IP pool" for two unrelated things. Both come up when you're doing backplane/segmentation work, but they address completely different traffic.
Segmentation IP poolAHV VM network IPAM pool
AddressesCVM (and host) backplane/service vNICsUser VMs on an AHV-managed network
Configured inSettings → Network Configuration → Internal Interfaces (or Prism Central Network Segmentation)Prism → Network Config → the VM subnet, or `acli`
Routable?No for Backplane, yes for Service/DRDepends on the VM network's own VLAN
AssignmentAutomatic, one IP per CVM/host, no DHCP involvedNutanix-managed DHCP hands addresses to VMs on boot
#### Segmentation IP pool (Backplane / Service) When you enable Backplane or Service segmentation, Prism asks for a start/end range, e.g.: ``` 192.168.21.11 - 192.168.21.20 ``` Size it for the cluster's current node count plus headroom for future expansion — one address is consumed per CVM (and, on current AOS, per AHV host) for each segmented traffic type. There's no reuse or lease/DHCP mechanism here: once an address is assigned it stays assigned until the interface is reconfigured. #### AHV VM network IPAM pool Separate from the above — this is Nutanix-managed DHCP for guest VMs on a given AHV network, already referenced on *Important Commands* in this book: ```bash acli net.create vlan= ip_config= ``` The command above only creates the network/subnet — the actual address pool for it is added separately: ```bash acli net.add_dhcp_pool start= end= ``` or in Prism: the VM network's config page → "IP Address Pools" → Create Pool. **Gotcha:** `.254` in the subnet is reserved for the Acropolis DHCP server itself if you didn't explicitly set a DHCP server address when creating the network — don't include it in the pool range. This pool has nothing to do with the CVM/host backplane above — it only ever hands out addresses to VMs that sit on this particular AHV network. # AHV Networks (acli) #### AHV Networks (acli) List all AHV networks ```bash acli net.list ``` Create a new VLAN network ```bash acli net.create vlan= ``` Create a network with IPAM (Nutanix-managed DHCP) ```bash acli net.create vlan= ip_config= ``` Create NIC with Intel E100: ``` acli vm.nic_create network= mac= model=e1000 ``` # Open vSwitch #### Open vSwitch (on the AHV host) Show a host's uplink configuration ```bash manage_ovs show_uplinks ``` Adjust uplinks ```bash manage_ovs --interfaces eth0,eth1 update_uplinks ``` Show bridges and ports ```bash ovs-vsctl show ``` Show bonding status ```bash ovs-appctl bond/show ``` # IP / Routing & Crash Cart #### IP / Routing (CVM) Default gateway and routing table on a CVM ```bash netstat -rn ``` List ARP entries ```bash arp -n ``` Delete a single ARP entry ```bash arp -d x.x.x.x ``` Flush the entire ARP cache ```bash ip -s -s neigh flush all ``` #### Host IP manuell setzen (Crash Cart) Manuelle IP-Konfiguration pro AHV-Host, z. B. wenn der Host per Konsole/IPMI erreichbar ist aber (noch) kein Netzwerk hat ```bash /usr/local/bin/network-crashcart ```