Replace multicast address with class E (#5051)

Ignoring unrelated broken link.

* Replace multicast address with class E

* address comments

* Update content/en/docs/setup/install/multicluster/gateways/index.md

Co-Authored-By: Frank Budinsky <frankb@ca.ibm.com>

* Update content/en/docs/setup/install/multicluster/gateways/index.md

Co-Authored-By: Frank Budinsky <frankb@ca.ibm.com>

* Update content/en/docs/setup/install/multicluster/gateways/index.md

Co-Authored-By: Frank Budinsky <frankb@ca.ibm.com>

.spelling

@@ -345,7 +345,7 @@ misordered
 Mitigations
 MongoDB
 mongodb
-multicast
+Multicast
 Multicloud
 multicloud
 Multicluster

content/en/blog/2019/multicluster-version-routing/index.md

@@ -299,7 +299,7 @@ spec:
     protocol: http
   resolution: DNS
   addresses:
-  - 224.0.0.3
+  - 240.0.0.3
   endpoints:
   - address: ${CLUSTER2_GW_ADDR}
     labels:
@@ -326,9 +326,8 @@ spec:
 EOF
 {{< /text >}}
 
-The address `224.0.0.3` of the service entry can be any arbitrary unallocated IP.
+The address `240.0.0.3` of the service entry can be any arbitrary unallocated IP.
-Note that loopback range `127.0.0.0/8` should not be used, as it will influence outbound traffic.
+Using an IP from the class E addresses range 240.0.0.0/4 is a good choice.
-Using an IP from the multicast range 224.0.0.0/4 is a good choice.
 Check out the
 [gateway-connected multicluster example](/docs/setup/install/multicluster/gateways/#configure-the-example-services)
 for more details.

content/en/docs/setup/install/multicluster/gateways/index.md

@@ -264,11 +264,15 @@ running in a second cluster. Before you begin:
     {{< /tip >}}
 
     If the global services have actual VIPs, you can use those, but otherwise we suggest
-    using IPs from the multicast range `224.0.0.0/4` that are not already allocated.
+    using IPs from the class E addresses range `240.0.0.0/4`.
-    These IPs are not loopback addresses and are non-routable outside of a pod.
     Application traffic for these IPs will be captured by the sidecar and routed to the
     appropriate remote service.
 
+    {{< warning >}}
+    Multicast addresses (224.0.0.0 ~ 239.255.255.255) should not be used because there is no route to them by default.
+    Loopback addresses (127.0.0.0/8) should also not be used because traffic sent to them may be redirected to the sidecar inbound listener.
+    {{< /warning >}}
+
     {{< text bash >}}
     $ kubectl apply --context=$CTX_CLUSTER1 -n foo -f - <<EOF
     apiVersion: networking.istio.io/v1alpha3
@@ -292,7 +296,7 @@ running in a second cluster. Before you begin:
       # must be unique for each remote service, within a given cluster.
       # This address need not be routable. Traffic for this IP will be captured
       # by the sidecar and routed appropriately.
-      - 224.0.0.2
+      - 240.0.0.2
       endpoints:
       # This is the routable address of the ingress gateway in cluster2 that
       # sits in front of sleep.foo service. Traffic from the sidecar will be
@@ -363,7 +367,7 @@ spec:
     protocol: http
   resolution: STATIC
   addresses:
-  - 224.0.0.2
+  - 240.0.0.2
   endpoints:
   - address: ${CLUSTER2_GW_ADDR}
     network: external
@@ -397,7 +401,7 @@ spec:
     protocol: http
   resolution: DNS
   addresses:
-  - 224.0.0.2
+  - 240.0.0.2
   endpoints:
   - address: ${CLUSTER2_GW_ADDR}
     network: external
@@ -457,7 +461,7 @@ spec:
   addresses:
   # the IP address to which httpbin.bar.global will resolve to
   # must be unique for each service.
-  - 224.0.0.2
+  - 240.0.0.2
   endpoints:
   - address: ${CLUSTER2_GW_ADDR}
     labels: