Fix IPv6 validation when VM gets route advertisements

For unknown reasons right now, on 456.x stemcells, the VM was not
receiving route advertisements, or was not assigning ipv6 addresses
received via the route advertiser. On newer stemcells, this was
happening and led to interfaces like eth1 having multiple IP addresses.

This broke in two places:
* arping: this does not exist for ipv6 and the replacement is ndp
(neighbor discovery protocol). For this commit, just ignore ipv6
addresses
* ip addr validation: bosh-agent validates that the IP assigned by the
bosh-director is actually configured on an interface. The previous logic
used the first address configured on the interface instead of
enumerating through all addresses. An example error message from
`/var/vcap/bosh/log/current`:

```
Validating network interface 'eth1' IP addresses, expected: '2601:0646:0100:69f5:0000:0000:0000:0001', actual: '2601:0646:0100:69f5:0102:03ff:fe04:0506'
```

While `ip a` would show something like:

```
1: eth1: ...
    link/ether ...
    inet6 2601:0646:0100:69f5:0102:03ff:fe04:0506/64 scope global dynamic mngtmpaddr noprefixroute
       valid_lft 2591996sec preferred_lft 604796sec
    inet6 2601:0646:0100:69f5:0000:0000:0000:0001/64 scope global temporary dynamic
       valid_lft 588658sec preferred_lft 70072sec

```

Here, the bosh-agent only used the first entry as the "actual assigned
IP", which is incorrect.

[#169694744](https://www.pivotaltracker.com/story/show/169694744)

Co-authored-by: Brian Cunnie <bcunnie@pivotal.io>

platform/net/arp/arping.go

@@ -1,6 +1,7 @@
 package arp
 
 import (
+	"net"
 	"path"
 	"sync"
 	"time"
@@ -47,6 +48,16 @@ func (a arping) BroadcastMACAddresses(addresses []boship.InterfaceAddress) {
 	var wg sync.WaitGroup
 
 	for _, addr := range addresses {
+		ip, err := addr.GetIP()
+		if err != nil {
+			continue
+		}
+
+		formattedIP := net.ParseIP(ip)
+		if formattedIP.To4() == nil {
+			continue
+		}
+
 		wg.Add(1) // Outside of goroutine
 
 		go func(address boship.InterfaceAddress) {

platform/net/arp/arping_test.go

@@ -79,5 +79,14 @@ var _ = Describe("arping", func() {
 			arping.BroadcastMACAddresses(addresses)
 			Expect(cmdRunner.RunCommands).To(BeEmpty())
 		})
+
+		It("ignores ipv6 addresses", func() {
+			addresses := []boship.InterfaceAddress{
+				boship.NewSimpleInterfaceAddress("eth0", "fe80::"),
+			}
+
+			arping.BroadcastMACAddresses(addresses)
+			Expect(len(cmdRunner.RunCommands)).To(Equal(0))
+		})
 	})
 })

platform/net/ip/interface_addresses_validator.go

@@ -1,6 +1,8 @@
 package ip
 
 import (
+	"strings"
+
 	bosherr "github.com/cloudfoundry/bosh-utils/errors"
 )
 
@@ -27,28 +29,35 @@ func (i *interfaceAddressesValidator) Validate(desiredInterfaceAddresses []Inter
 	for _, desiredInterfaceAddress := range desiredInterfaceAddresses {
 		ifaceName := desiredInterfaceAddress.GetInterfaceName()
 
-		iface, found := i.findInterfaceByName(ifaceName, systemInterfaceAddresses)
-		if !found {
+		ifaces := i.findInterfaceByName(ifaceName, systemInterfaceAddresses)
+		if len(ifaces) == 0 {
 			return bosherr.Errorf("Validating network interface '%s' IP addresses, no interface configured with that name", ifaceName)
 		}
 
+		actualIPs := []string{}
 		desiredIP, _ := desiredInterfaceAddress.GetIP()
-		actualIP, _ := iface.GetIP()
+		for _, iface := range ifaces {
+			actualIP, _ := iface.GetIP()
 
-		if desiredIP != actualIP {
-			return bosherr.Errorf("Validating network interface '%s' IP addresses, expected: '%s', actual: '%s'", ifaceName, desiredIP, actualIP)
+			if desiredIP == actualIP {
+				return nil
+			}
+			actualIPs = append(actualIPs, actualIP)
 		}
+
+		return bosherr.Errorf("Validating network interface '%s' IP addresses, expected: '%s', actual: [%s]", ifaceName, desiredIP, strings.Join(actualIPs, ", "))
 	}
 
 	return nil
 }
 
-func (i *interfaceAddressesValidator) findInterfaceByName(ifaceName string, ifaces []InterfaceAddress) (InterfaceAddress, bool) {
+func (i *interfaceAddressesValidator) findInterfaceByName(ifaceName string, ifaces []InterfaceAddress) []InterfaceAddress {
+	result := []InterfaceAddress{}
 	for _, iface := range ifaces {
 		if iface.GetInterfaceName() == ifaceName {
-			return iface, true
+			result = append(result, iface)
 		}
 	}
 
-	return nil, false
+	return result
 }

platform/net/ip/interface_addresses_validator_test.go

@@ -32,7 +32,22 @@ var _ = Describe("InterfaceAddressesValidator", func() {
 		It("returns nil", func() {
 			err := interfaceAddrsValidator.Validate([]boship.InterfaceAddress{
 				boship.NewSimpleInterfaceAddress("eth0", "1.2.3.4"),
-				boship.NewSimpleInterfaceAddress("eth1", "5.6.7.8"),
+			})
+			Expect(err).ToNot(HaveOccurred())
+		})
+	})
+
+	Context("when an interface has multiple IPs", func() {
+		BeforeEach(func() {
+			interfaceAddrsProvider.GetInterfaceAddresses = []boship.InterfaceAddress{
+				boship.NewSimpleInterfaceAddress("eth0", "1.2.3.4"),
+				boship.NewSimpleInterfaceAddress("eth0", "fe80::1"),
+			}
+		})
+
+		It("returns nil", func() {
+			err := interfaceAddrsValidator.Validate([]boship.InterfaceAddress{
+				boship.NewSimpleInterfaceAddress("eth0", "fe80::1"),
 			})
 			Expect(err).ToNot(HaveOccurred())
 		})
@@ -42,6 +57,7 @@ var _ = Describe("InterfaceAddressesValidator", func() {
 		BeforeEach(func() {
 			interfaceAddrsProvider.GetInterfaceAddresses = []boship.InterfaceAddress{
 				boship.NewSimpleInterfaceAddress("eth0", "1.2.3.5"),
+				boship.NewSimpleInterfaceAddress("eth0", "1.2.3.6"),
 			}
 		})
 
@@ -50,7 +66,7 @@ var _ = Describe("InterfaceAddressesValidator", func() {
 				boship.NewSimpleInterfaceAddress("eth0", "1.2.3.4"),
 			})
 			Expect(err).To(HaveOccurred())
-			Expect(err.Error()).To(ContainSubstring("Validating network interface 'eth0' IP addresses, expected: '1.2.3.4', actual: '1.2.3.5'"))
+			Expect(err.Error()).To(ContainSubstring("Validating network interface 'eth0' IP addresses, expected: '1.2.3.4', actual: [1.2.3.5, 1.2.3.6]"))
 		})
 	})
 
@@ -83,15 +99,4 @@ var _ = Describe("InterfaceAddressesValidator", func() {
 			Expect(err.Error()).To(ContainSubstring("Validating network interface 'eth0' IP addresses, no interface configured with that name"))
 		})
 	})
-
-	Context("when resolv.conf has valid dns configurations", func() {
-		It("fails", func() {
-
-		})
-
-	})
-
-	Context("when resolv.conf has invalid dns configurations", func() {
-
-	})
 })