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IP Masquerade Agent User Guide

This page shows how to configure and enable the ip-masq-agent.

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube, or you can use one of these Kubernetes playgrounds:

Create an ip-masq-agent

To create an ip-masq-agent, run the following kubectl command:

kubectl create -f https://raw.githubusercontent.com/kubernetes-incubator/ip-masq-agent/master/ip-masq-agent.yaml

You must also apply the appropriate node label to any nodes in your cluster that you want the agent to run on.

kubectl label nodes my-node beta.kubernetes.io/masq-agent-ds-ready=true

More information can be found in the ip-masq-agent documentation here

In most cases, the default set of rules should be sufficient; however, if this is not the case for your cluster, you can create and apply a ConfigMap to customize the IP ranges that are affected. For example, to allow only 10.0.0.0/8 to be considered by the ip-masq-agent, you can create the following ConfigMap in a file called “config”. Note: It is important that the file is called config since, by default, that will be used as the key for lookup by the ip-masq-agent:

nonMasqueradeCIDRs:
  - 10.0.0.0/8
resyncInterval: 60s

Run the following command to add the config map to your cluster:

kubectl create configmap ip-masq-agent --from-file=config --namespace=kube-system

This will update a file located at /etc/config/ip-masq-agent which is periodically checked every resyscInterval and applied to the cluster node. After the resync interval has expired, you should see the iptables rules reflect your changes:

iptables -t nat -L IP-MASQ-AGENT
Chain IP-MASQ-AGENT (1 references)
target     prot opt source               destination         
RETURN     all  --  anywhere             169.254.0.0/16       /* ip-masq-agent: cluster-local traffic should not be subject to MASQUERADE */ ADDRTYPE match dst-type !LOCAL
RETURN     all  --  anywhere             10.0.0.0/8           /* ip-masq-agent: cluster-local
MASQUERADE  all  --  anywhere             anywhere             /* ip-masq-agent: outbound traffic should be subject to MASQUERADE (this match must come after cluster-local CIDR matches) */ ADDRTYPE match dst-type !LOCAL

By default, the link local range (169.254.0.0/16) is also handled by the ip-masq agent, which sets up the appropriate iptables rules. To have the ip-masq-agent ignore link local, you can set masqLinkLocal to true in the config map.

nonMasqueradeCIDRs:
  - 10.0.0.0/8
resyncInterval: 60s
masqLinkLocal: true

IP Masquerade Agent User Guide

The ip-masq-agent configures iptables rules to hide a pod’s IP address behind the cluster node’s IP address. This is typically done when sending traffic to destinations outside the cluster’s pod CIDR range.

Key Terms

The ip-masq-agent configures iptables rules to handle masquerading node/pod IP addresses when sending traffic to destinations outside the cluster node’s IP and the Cluster IP range. This essentially hides pod IP addresses behind the cluster node’s IP address. In some environments, traffic to “external” addresses must come from a known machine address. For example, in Google Cloud, any traffic to the internet must come from a VM’s IP. When containers are used, as in GKE, the Pod IP will be rejected for egress. To avoid this, we must hide the Pod IP behind the VM’s own IP address - generally known as “masquerade”. By default, the agent is configured to treat the three private IP ranges specified by RFC 1918 as non-masquerade CIDR. These ranges are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. The agent will also treat link-local (169.254.0.0/16) as a non-masquerade CIDR by default. The agent is configured to reload its configuration from the location /etc/config/ip-masq-agent every 60 seconds, which is also configurable.

masq/non-masq example

The agent configuration file must be written in YAML or JSON syntax, and may contain three optional keys:

Traffic to 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16) ranges will NOT be masqueraded. Any other traffic (assumed to be internet) will be masqueraded. An example of a local destination from a pod could be its Node’s IP address as well as another node’s address or one of the IP addresses in Cluster’s IP range. Any other traffic will be masqueraded by default. The below entries show the default set of rules that are applied by the ip-masq-agent:

iptables -t nat -L IP-MASQ-AGENT
RETURN     all  --  anywhere             169.254.0.0/16       /* ip-masq-agent: cluster-local traffic should not be subject to MASQUERADE */ ADDRTYPE match dst-type !LOCAL
RETURN     all  --  anywhere             10.0.0.0/8           /* ip-masq-agent: cluster-local traffic should not be subject to MASQUERADE */ ADDRTYPE match dst-type !LOCAL
RETURN     all  --  anywhere             172.16.0.0/12        /* ip-masq-agent: cluster-local traffic should not be subject to MASQUERADE */ ADDRTYPE match dst-type !LOCAL
RETURN     all  --  anywhere             192.168.0.0/16       /* ip-masq-agent: cluster-local traffic should not be subject to MASQUERADE */ ADDRTYPE match dst-type !LOCAL
MASQUERADE  all  --  anywhere             anywhere             /* ip-masq-agent: outbound traffic should be subject to MASQUERADE (this match must come after cluster-local CIDR matches) */ ADDRTYPE match dst-type !LOCAL

By default, in GCE/GKE starting with Kubernetes version 1.7.0, if network policy is enabled or you are using a cluster CIDR not in the 10.0.0.0/8 range, the ip-masq-agent will run in your cluster. If you are running in another environment, you can add the ip-masq-agent DaemonSet to your cluster:

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