diff --git a/src/Parser.c b/src/Parser.c
index bef70af..3dda8a0 100644
--- a/src/Parser.c
+++ b/src/Parser.c
@@ -24,12 +24,18 @@
 
 #include <Parser.h>
 
-#include <Cytoplasm/Str.h>
 #include <Cytoplasm/Memory.h>
+#include <Cytoplasm/Str.h>
+#include <Cytoplasm/Int.h>
 
 #include <string.h>
+#include <stdlib.h>
 #include <ctype.h>
 
+
+/* Iterate through a char **. */
+#define Iterate(s) (*(*s)++)
+
 /* Parse an extended localpart */
 static int
 ParseUserLocalpart(char **str, char **out)
@@ -45,21 +51,187 @@ ParseUserLocalpart(char **str, char **out)
     /* An extended localpart contains every ASCII printable character, 
      * except an ':'. */
     start = *str;
-    while (isascii((c = (*(*str)++))) && c != ':' && c)
+    while (isascii((c = Iterate(str))) && c != ':' && c)
     {
         /* Do nothing */
     }
-    length = (size_t) (*str - start) -1;
-    if (c != ':' || length < 1)
+    length = (size_t) (*str - start) - 1;
+    if (length < 1)
     {
         *str = start;
         return 0;
     }
+    if (c == ':')
+    {
+        --(*str);
+    }
 
     *out = Malloc(length + 1);
     memcpy(*out, start, length);
-    *out[length] = '\0';
+    (*out)[length] = '\0';
 
+    return 1;
+}
+/* Parses an IPv4 address. */
+static int
+ParseIPv4(char **str, char **out)
+{
+    /* Be *very* careful with this buffer */
+    char buffer[4];
+    char *start;
+    size_t length;
+    char c;
+
+    int digit = 0;
+    int digits = 0;
+
+    memset(buffer, '\0', 4);
+    start = *str;
+
+    /* An IPv4 address is made of 4 blocks between 1-3 digits, like so:
+     * (1-3)*DIGIT.(1-3)*DIGIT.(1-3)*DIGIT.(1-3)*DIGIT */
+    while ((isdigit(c = Iterate(str)) || c == '.') && c && digits < 4)
+    {
+        if (isdigit(c))
+        {
+            digit++;
+            continue;
+        }
+        if (digit < 1 || digit > 3)
+        {
+            /* Current digit is too long for the spec! */
+            *str = start;
+            return 0;
+        }
+        memcpy(buffer, *str - digit - 1, digit);
+        if (atoi(buffer) > 255)
+        {
+            /* Current digit is too large for the spec! */
+            *str = start;
+            return 0;
+        }
+        memset(buffer, '\0', 4);
+        digit = 0;
+        digits++; /* We have parsed a digit. */
+    }
+    if (c == '.' || digits != 3)
+    {
+        *str = start;
+        return 0;
+    }
+    length = (size_t) (*str - start) - 1;
+    *out = Malloc(length + 1);
+    memcpy(*out, start, length);
+    (*str)--;
+    return 1;
+}
+static int
+ParseIPv6(char **str, char **out)
+{
+    /* TODO */
+    (void) str;
+    (void) out;
+    return 0;
+}
+static int
+ParseHostname(char **str, char **out)
+{
+    char *start;
+    size_t length = 0;
+    char c;
+
+    start = *str;
+    while ((c = Iterate(str)) && 
+        (isalnum(c) || c == '.' || c == '-') && 
+        ++length < 256)
+    {
+        /* Do nothing. */
+    }
+    if (length < 1 || length > 255)
+    {
+        *str = start;
+        return 0;
+    }
+    length = (size_t) (*str - start) - 1;
+    *out = Malloc(length + 1);
+    memcpy(*out, start, length);
+    (*str)--;
+    return 1;
+}
+
+static int
+ParseServerName(char **str, ServerPart *out)
+{
+    char c;
+    char *start;
+    char *startPort;
+    size_t chars = 0;
+
+    char *host = NULL;
+    char *port = NULL;
+
+    if (!str || !out)
+    {
+        return 0;
+    }
+
+    start = *str;
+
+    if (!host)
+    {
+        /* If we can parse an IPv4 address, use that. */
+        ParseIPv4(str, &host);
+    }
+    if (!host)
+    {
+        /* If we can parse an IPv6 address, use that. */
+        ParseIPv6(str, &host);
+    }
+    if (!host)
+    {
+        /* If we can parse an hostname, use that. */
+        ParseHostname(str, &host);
+    }
+    if (!host)
+    {
+        /* Can't parse a valid server name. */
+        return 0;
+    }
+    /* Now, there's only 2 options: a ':', or the end(everything else.) */
+    if (**str != ':')
+    {
+        /* We're done. */
+        out->hostname = host;
+        out->port = NULL;
+        return 1;
+    }
+    /* TODO: Separate this out */
+    startPort = ++(*str);
+    while(isdigit(c = Iterate(str)) && c && ++chars < 5)
+    {
+        /* Do nothing. */
+    }
+    if (chars < 1 || chars > 5)
+    {
+        *str = start;
+        Free(host);
+        host = NULL;
+        return 0;
+    }
+
+    port = Malloc(chars + 1);
+    memcpy(port, startPort, chars);
+    port[chars] = '\0';
+    if (atol(port) > 65535)
+    {
+        Free(port);
+        Free(host);
+        *str = start;
+        return 0;
+    }
+
+    out->hostname = host;
+    out->port = port;
 
     return 1;
 }
@@ -89,17 +261,48 @@ ParseCommonID(char *str, CommonID *id)
         return 0;
     }
     id->sigil = sigil;
+    id->local = NULL;
+    id->server.hostname = NULL;
+    id->server.port = NULL;
     
-    switch(sigil)
+    switch (sigil)
     {
         case '@':
             if (!ParseUserLocalpart(&str, &id->local))
             {
                 return 0;
             }
+            if (*str++ != ':')
+            {
+                Free(id->local);
+                id->local = NULL;
+                return 0;
+            }
             /* TODO: Match whenever str is valid. */
-            id->server = StrDuplicate(str);
+            if (!ParseServerName(&str, &id->server))
+            {
+                Free(id->local);
+                id->local = NULL;
+                return 0;
+            }
             break;
     }
     return 1;
 }
+
+void
+CommonIDFree(CommonID id)
+{
+    if (id.local)
+    {
+        Free(id.local);
+    }
+    if (id.server.hostname)
+    {
+        Free(id.server.hostname);
+    }
+    if (id.server.port)
+    {
+        Free(id.server.port);
+    }
+}
diff --git a/src/User.c b/src/User.c
index 0f0f892..20a4289 100644
--- a/src/User.c
+++ b/src/User.c
@@ -909,29 +909,30 @@ UserIdParse(char *id, char *defaultServer)
     /* Fully-qualified user ID */
     if (*id == '@')
     {
+        /* TODO: Just use the CommonID. */
         CommonID commonID;
         commonID.sigil = '\0';
         commonID.local = NULL;
-        commonID.server = NULL;
-        if (!ParseCommonID(id, &commonID) || !commonID.server)
+        commonID.server.hostname = NULL;
+        commonID.server.port = NULL;
+        if (!ParseCommonID(id, &commonID) || !commonID.server.hostname)
         {
             Free(userId);
             Free(commonID.local);
-            Free(commonID.server);
-            userId = NULL;
-            goto finish;
-        }
-        if (*commonID.server == '\0')
-        {
-            Free(userId);
-            Free(commonID.local);
-            Free(commonID.server);
+            if (commonID.server.hostname)
+            {
+                Free(commonID.server.hostname);
+            }
             userId = NULL;
             goto finish;
         }
 
         userId->localpart = commonID.local;
-        userId->server = commonID.server;
+        userId->server = commonID.server.hostname;
+        if (commonID.server.port)
+        {
+            Free(commonID.server.port);
+        }
     }
     else
     {
diff --git a/src/include/Parser.h b/src/include/Parser.h
index 3f7fb7e..788f92f 100644
--- a/src/include/Parser.h
+++ b/src/include/Parser.h
@@ -36,6 +36,13 @@
  * Matrix specification
  */
 
+/**
+ * The host[:port] format in a servername.
+ */
+typedef struct ServerPart {
+    char *hostname;
+    char *port;
+} ServerPart;
 /**
  * A common identifier in the form '&local[:server]', where 
  * & determines the *type* of the identifier.
@@ -43,7 +50,7 @@
 typedef struct CommonID {
     char sigil;
     char *local;
-    char *server; /* Might be NULL for some sigils(e.g: room IDs >= v3) */
+    ServerPart server;
 } CommonID;
 
 /**