cli/sdk: Allow redirection to a different consul dns port (#15050)

.changelog/15050.txt

@@ -0,0 +1,6 @@
+```release-note:feature
+cli: Add `-consul-dns-port` flag to the `consul connect redirect-traffic` command to allow forwarding DNS traffic to a specific Consul DNS port.
+```
+```release-note:feature
+sdk: Configure `iptables` to forward DNS traffic to a specific DNS port.
+```

command/connect/redirecttraffic/redirect_traffic.go

@@ -38,6 +38,7 @@ type cmd struct {
 	// Flags.
 	nodeName             string
 	consulDNSIP          string
+	consulDNSPort        int
 	proxyUID             string
 	proxyID              string
 	proxyInboundPort     int
@@ -55,6 +56,7 @@ func (c *cmd) init() {
 	c.flags.StringVar(&c.nodeName, "node-name", "",
 		"The node name where the proxy service is registered. It requires proxy-id to be specified. This is needed if running in an environment without client agents.")
 	c.flags.StringVar(&c.consulDNSIP, "consul-dns-ip", "", "IP used to reach Consul DNS. If provided, DNS queries will be redirected to Consul.")
+	c.flags.IntVar(&c.consulDNSPort, "consul-dns-port", 0, "Port used to reach Consul DNS. If provided, DNS queries will be redirected to Consul.")
 	c.flags.StringVar(&c.proxyUID, "proxy-uid", "", "The user ID of the proxy to exclude from traffic redirection.")
 	c.flags.StringVar(&c.proxyID, "proxy-id", "", "The service ID of the proxy service registered with Consul.")
 	c.flags.IntVar(&c.proxyInboundPort, "proxy-inbound-port", 0, "The inbound port that the proxy is listening on.")
@@ -136,6 +138,7 @@ type trafficRedirectProxyConfig struct {
 func (c *cmd) generateConfigFromFlags() (iptables.Config, error) {
 	cfg := iptables.Config{
 		ConsulDNSIP:       c.consulDNSIP,
+		ConsulDNSPort:     c.consulDNSPort,
 		ProxyUserID:       c.proxyUID,
 		ProxyInboundPort:  c.proxyInboundPort,
 		ProxyOutboundPort: c.proxyOutboundPort,

command/connect/redirecttraffic/redirect_traffic_test.go

@@ -128,13 +128,14 @@ func TestGenerateConfigFromFlags(t *testing.T) {
 			},
 		},
 		{
-			name: "proxyID with Consul DNS IP provided",
+			name: "proxyID with Consul DNS IP and port provided",
 			command: func() cmd {
 				var c cmd
 				c.init()
 				c.proxyUID = "1234"
 				c.proxyID = "test-proxy-id"
 				c.consulDNSIP = "10.0.34.16"
+				c.consulDNSPort = 8600
 				return c
 			},
 			consulServices: []api.AgentServiceRegistration{
@@ -151,6 +152,7 @@ func TestGenerateConfigFromFlags(t *testing.T) {
 			},
 			expCfg: iptables.Config{
 				ConsulDNSIP:       "10.0.34.16",
+				ConsulDNSPort:     8600,
 				ProxyUserID:       "1234",
 				ProxyInboundPort:  20000,
 				ProxyOutboundPort: iptables.DefaultTProxyOutboundPort,

sdk/iptables/iptables.go

@@ -2,6 +2,7 @@ package iptables
 
 import (
 	"errors"
+	"fmt"
 	"strconv"
 )
 
@@ -30,6 +31,9 @@ type Config struct {
 	// ConsulDNSIP is the IP for Consul DNS to direct DNS queries to.
 	ConsulDNSIP string
 
+	// ConsulDNSPort is the port for Consul DNS to direct DNS queries to.
+	ConsulDNSPort int
+
 	// ProxyUserID is the user ID of the proxy process.
 	ProxyUserID string
 
@@ -107,7 +111,7 @@ func Setup(cfg Config) error {
 		cfg.IptablesProvider.AddRule("iptables", "-t", "nat", "-A", ProxyOutputRedirectChain, "-p", "tcp", "-j", "REDIRECT", "--to-port", strconv.Itoa(cfg.ProxyOutboundPort))
 
 		// The DNS rules are applied before the rules that directs all TCP traffic, so that the traffic going to port 53 goes through this rule first.
-		if cfg.ConsulDNSIP != "" {
+		if cfg.ConsulDNSIP != "" && cfg.ConsulDNSPort == 0 {
 			// Traffic in the DNSChain is directed to the Consul DNS Service IP.
 			cfg.IptablesProvider.AddRule("iptables", "-t", "nat", "-A", DNSChain, "-p", "udp", "--dport", "53", "-j", "DNAT", "--to-destination", cfg.ConsulDNSIP)
 			cfg.IptablesProvider.AddRule("iptables", "-t", "nat", "-A", DNSChain, "-p", "tcp", "--dport", "53", "-j", "DNAT", "--to-destination", cfg.ConsulDNSIP)
@@ -115,6 +119,19 @@ func Setup(cfg Config) error {
 			// For outbound TCP and UDP traffic going to port 53 (DNS), jump to the DNSChain.
 			cfg.IptablesProvider.AddRule("iptables", "-t", "nat", "-A", "OUTPUT", "-p", "udp", "--dport", "53", "-j", DNSChain)
 			cfg.IptablesProvider.AddRule("iptables", "-t", "nat", "-A", "OUTPUT", "-p", "tcp", "--dport", "53", "-j", DNSChain)
+		} else if cfg.ConsulDNSPort != 0 {
+			consulDNSIP := "127.0.0.1"
+			if cfg.ConsulDNSIP != "" {
+				consulDNSIP = cfg.ConsulDNSIP
+			}
+			consulDNSHostPort := fmt.Sprintf("%s:%d", consulDNSIP, cfg.ConsulDNSPort)
+			// Traffic in the DNSChain is directed to the Consul DNS Service IP.
+			cfg.IptablesProvider.AddRule("iptables", "-t", "nat", "-A", DNSChain, "-p", "udp", "-d", consulDNSIP, "--dport", "53", "-j", "DNAT", "--to-destination", consulDNSHostPort)
+			cfg.IptablesProvider.AddRule("iptables", "-t", "nat", "-A", DNSChain, "-p", "tcp", "-d", consulDNSIP, "--dport", "53", "-j", "DNAT", "--to-destination", consulDNSHostPort)
+
+			// For outbound TCP and UDP traffic going to port 53 (DNS), jump to the DNSChain. Only redirect traffic that's going to consul's DNS IP.
+			cfg.IptablesProvider.AddRule("iptables", "-t", "nat", "-A", "OUTPUT", "-p", "udp", "-d", consulDNSIP, "--dport", "53", "-j", DNSChain)
+			cfg.IptablesProvider.AddRule("iptables", "-t", "nat", "-A", "OUTPUT", "-p", "tcp", "-d", consulDNSIP, "--dport", "53", "-j", DNSChain)
 		}
 
 		// For outbound TCP traffic jump from OUTPUT chain to PROXY_OUTPUT chain.

sdk/iptables/iptables_test.go

@@ -64,6 +64,63 @@ func TestSetup(t *testing.T) {
 				"iptables -t nat -A CONSUL_PROXY_INBOUND -p tcp -j CONSUL_PROXY_IN_REDIRECT",
 			},
 		},
+		{
+			"Consul DNS port provided",
+			Config{
+				ProxyUserID:      "123",
+				ProxyInboundPort: 20000,
+				ConsulDNSPort:    8600,
+				IptablesProvider: &fakeIptablesProvider{},
+			},
+			[]string{
+				"iptables -t nat -N CONSUL_PROXY_INBOUND",
+				"iptables -t nat -N CONSUL_PROXY_IN_REDIRECT",
+				"iptables -t nat -N CONSUL_PROXY_OUTPUT",
+				"iptables -t nat -N CONSUL_PROXY_REDIRECT",
+				"iptables -t nat -N CONSUL_DNS_REDIRECT",
+				"iptables -t nat -A CONSUL_PROXY_REDIRECT -p tcp -j REDIRECT --to-port 15001",
+				"iptables -t nat -A CONSUL_DNS_REDIRECT -p udp -d 127.0.0.1 --dport 53 -j DNAT --to-destination 127.0.0.1:8600",
+				"iptables -t nat -A CONSUL_DNS_REDIRECT -p tcp -d 127.0.0.1 --dport 53 -j DNAT --to-destination 127.0.0.1:8600",
+				"iptables -t nat -A OUTPUT -p udp -d 127.0.0.1 --dport 53 -j CONSUL_DNS_REDIRECT",
+				"iptables -t nat -A OUTPUT -p tcp -d 127.0.0.1 --dport 53 -j CONSUL_DNS_REDIRECT",
+				"iptables -t nat -A OUTPUT -p tcp -j CONSUL_PROXY_OUTPUT",
+				"iptables -t nat -A CONSUL_PROXY_OUTPUT -m owner --uid-owner 123 -j RETURN",
+				"iptables -t nat -A CONSUL_PROXY_OUTPUT -d 127.0.0.1/32 -j RETURN",
+				"iptables -t nat -A CONSUL_PROXY_OUTPUT -j CONSUL_PROXY_REDIRECT",
+				"iptables -t nat -A CONSUL_PROXY_IN_REDIRECT -p tcp -j REDIRECT --to-port 20000",
+				"iptables -t nat -A PREROUTING -p tcp -j CONSUL_PROXY_INBOUND",
+				"iptables -t nat -A CONSUL_PROXY_INBOUND -p tcp -j CONSUL_PROXY_IN_REDIRECT",
+			},
+		},
+		{
+			"Consul DNS IP and port provided",
+			Config{
+				ProxyUserID:      "123",
+				ProxyInboundPort: 20000,
+				ConsulDNSIP:      "10.0.34.16",
+				ConsulDNSPort:    8600,
+				IptablesProvider: &fakeIptablesProvider{},
+			},
+			[]string{
+				"iptables -t nat -N CONSUL_PROXY_INBOUND",
+				"iptables -t nat -N CONSUL_PROXY_IN_REDIRECT",
+				"iptables -t nat -N CONSUL_PROXY_OUTPUT",
+				"iptables -t nat -N CONSUL_PROXY_REDIRECT",
+				"iptables -t nat -N CONSUL_DNS_REDIRECT",
+				"iptables -t nat -A CONSUL_PROXY_REDIRECT -p tcp -j REDIRECT --to-port 15001",
+				"iptables -t nat -A CONSUL_DNS_REDIRECT -p udp -d 10.0.34.16 --dport 53 -j DNAT --to-destination 10.0.34.16:8600",
+				"iptables -t nat -A CONSUL_DNS_REDIRECT -p tcp -d 10.0.34.16 --dport 53 -j DNAT --to-destination 10.0.34.16:8600",
+				"iptables -t nat -A OUTPUT -p udp -d 10.0.34.16 --dport 53 -j CONSUL_DNS_REDIRECT",
+				"iptables -t nat -A OUTPUT -p tcp -d 10.0.34.16 --dport 53 -j CONSUL_DNS_REDIRECT",
+				"iptables -t nat -A OUTPUT -p tcp -j CONSUL_PROXY_OUTPUT",
+				"iptables -t nat -A CONSUL_PROXY_OUTPUT -m owner --uid-owner 123 -j RETURN",
+				"iptables -t nat -A CONSUL_PROXY_OUTPUT -d 127.0.0.1/32 -j RETURN",
+				"iptables -t nat -A CONSUL_PROXY_OUTPUT -j CONSUL_PROXY_REDIRECT",
+				"iptables -t nat -A CONSUL_PROXY_IN_REDIRECT -p tcp -j REDIRECT --to-port 20000",
+				"iptables -t nat -A PREROUTING -p tcp -j CONSUL_PROXY_INBOUND",
+				"iptables -t nat -A CONSUL_PROXY_INBOUND -p tcp -j CONSUL_PROXY_IN_REDIRECT",
+			},
+		},
 		{
 			"proxy outbound port is provided",
 			Config{

website/content/commands/connect/redirect-traffic.mdx

@@ -36,6 +36,8 @@ Usage: `consul connect redirect-traffic [options]`
 
 - `-consul-dns-ip` - The IP address of the Consul DNS resolver. If provided, DNS queries will be redirected to the provided IP address for name resolution.
 
+- `-consul-dns-port` - The port of the Consul DNS resolver. If provided, DNS queries will be redirected to the provided IP address for name resolution.
+
 - `-proxy-id` - The [proxy service](/docs/connect/registration/service-registration) ID.
   This service ID must already be registered with the local agent.