Fix grammar 'the administrator'

PR:		39093
Submitted by:	Mike Makonnen <makonnen@packbell.net>

share/man/man4/gif.4

@@ -64,44 +64,46 @@ variable in
 .Pp
 To use
 .Nm ,
-administrator needs to configure protocol and addresses used for the outer
+the administrator needs to configure the protocol and addresses used for the outer
 header.
 This can be done by using
 .Xr gifconfig 8 ,
 or
 .Dv SIOCSIFPHYADDR
 ioctl.
-Also, administrator needs to configure protocol and addresses used for the
+The administrator also needs to configure the protocol and addresses for the
-inner header, by using
+inner header, with
 .Xr ifconfig 8 .
-Note that IPv6 link-local address
+Note that IPv6 link-local addresses
-(those start with
+(those that start with
 .Li fe80:: )
-will be automatically configured whenever possible.
+will be automatically be configured whenever possible.
-You may need to remove IPv6 link-local address manually using
+You may need to remove IPv6 link-local addresses manually using
 .Xr ifconfig 8 ,
-when you would like to disable the use of IPv6 as inner header
+if you want to disable the use of IPv6 as the inner header
-(like when you need pure IPv4-over-IPv6 tunnel).
+(for example, if you need a pure IPv4-over-IPv6 tunnel).
-Finally, use routing table to route the packets toward
+Finally, you must modify the routing table to route the packets through the
 .Nm
 interface.
 .Pp
+The
 .Nm
-can be configured to be ECN friendly.
+pseudo-device can be configured to be ECN friendly.
 This can be configured by
 .Dv IFF_LINK1 .
 .Ss ECN friendly behavior
+The
 .Nm
-can be configured to be ECN friendly, as described in
+pseudo-device can be configured to be ECN friendly, as described in
 .Dv draft-ietf-ipsec-ecn-02.txt .
-This is turned off by default, and can be turned on by
+This is turned off by default, and can be turned on by the
 .Dv IFF_LINK1
 interface flag.
 .Pp
 Without
 .Dv IFF_LINK1 ,
 .Nm
-will show a normal behavior, like described in RFC2893.
+will show normal behavior, as described in RFC2893.
 This can be summarized as follows:
 .Bl -tag -width "Ingress" -offset indent
 .It Ingress
@@ -139,15 +141,15 @@ enable ECN CE bit on the inner.
 Note that the ECN friendly behavior violates RFC2893.
 This should be used in mutual agreement with the peer.
 .Ss Security
-Malicious party may try to circumvent security filters by using
+A malicious party may try to circumvent security filters by using
 tunnelled packets.
 For better protection,
 .Nm
-performs martian filter and ingress filter against outer source address,
+performs both martian and ingress filtering against the outer source address
 on egress.
-Note that martian/ingress filters are no way complete.
+Note that martian/ingress filters are in no way complete.
 You may want to secure your node by using packet filters.
-Ingress filter can be turned off by
+Ingress filtering can be turned off by
 .Dv IFF_LINK2
 bit.
 .\"
@@ -192,13 +194,13 @@ to 1.
 .Sh HISTORY
 The
 .Nm
-device first appeared in WIDE hydrangea IPv6 kit.
+device first appeared in the WIDE hydrangea IPv6 kit.
 .\"
 .Sh BUGS
-There are many tunnelling protocol specifications,
+There are many tunnelling protocol specifications, all
-defined differently from each other.
+defined differently from each other. The
 .Nm
-may not interoperate with peers which are based on different specifications,
+pseudo-device may not interoperate with peers which are based on different specifications,
 and are picky about outer header fields.
 For example, you cannot usually use
 .Nm
@@ -206,31 +208,32 @@ to talk with IPsec devices that use IPsec tunnel mode.
 .Pp
 The current code does not check if the ingress address
 (outer source address)
-configured to
+configured in the
 .Nm
-makes sense.
+interface makes sense.
-Make sure to configure an address which belongs to your node.
+Make sure to specify an address which belongs to your node.
 Otherwise, your node will not be able to receive packets from the peer,
-and your node will generate packets with a spoofed source address.
+and it will generate packets with a spoofed source address.
 .Pp
 If the outer protocol is IPv4,
 .Nm
 does not try to perform path MTU discovery for the encapsulated packet
 (DF bit is set to 0).
 .Pp
-If the outer protocol is IPv6, path MTU discovery for encapsulated packet
+If the outer protocol is IPv6, path MTU discovery for encapsulated packets
 may affect communication over the interface.
 The first bigger-than-pmtu packet may be lost.
 To avoid the problem, you may want to set the interface MTU for
 .Nm
-to 1240 or smaller, when outer header is IPv6 and inner header is IPv4.
+to 1240 or smaller, when the outer header is IPv6 and the inner header is IPv4.
 .Pp
+The
 .Nm
-does not translate ICMP messages for outer header into inner header.
+pseudo-device does not translate ICMP messages for the outer header into the inner header.
 .Pp
 In the past,
 .Nm
 had a multi-destination behavior, configurable via
 .Dv IFF_LINK0
 flag.
-The behavior was obsoleted and is no longer supported.
+The behavior is obsolete and is no longer supported.