diff --git a/docs/routing/babeld/maxlen-filter.md b/docs/routing/babeld/maxlen-filter.md
index e6cfeb6..8e7715d 100644
--- a/docs/routing/babeld/maxlen-filter.md
+++ b/docs/routing/babeld/maxlen-filter.md
@@ -1,6 +1,6 @@
 
 # Implement max-len filter
 
-To implement a max-length filter, we need a rule/policy/filter file that contains the corresponding prefixes with their maximum length. The entitydb contains a bash script `build_maxlen_filter.sh` for this purpose. If you run this script with the argument `babeld`, you will get a babeld-compatible list.
+To implement a max-length filter, we need a rule/policy/filter file that contains the corresponding prefixes with their maximum length. The entitydb contains a bash script `build_maxlen_filter.sh` for this purpose. If you run this script with the argument `babeld with-deny`, you will get a babeld-compatible list. The list includes rules to accept all maxlen-valid prefixes and filter all other CRXN prefixes.
 
-This list can now be inserted into the configuration file instead of `in ip fd00::/8 le 64 ge 44 allow`. It is recommended to automate this process.
+This list can now be saved in the configuration file before `in ip fd00::/8 le 64 ge 44 allow`. It is recommended to automate this process.
diff --git a/docs/routing/bird/maxlen-filter.md b/docs/routing/bird/maxlen-filter.md
index 17b74e7..31d09c0 100644
--- a/docs/routing/bird/maxlen-filter.md
+++ b/docs/routing/bird/maxlen-filter.md
@@ -1,23 +1,33 @@
 
 # Implement max-len filter
 
-To implement a max-length filter, we need a rule/policy/filter file that contains the corresponding prefixes with their maximum length. The entitydb contains a bash script `build_maxlen_filter.sh` for this purpose. If you run this script with the argument `bird`, you will get a bird-compatible list.
+To implement a max-length filter, we need a rule/policy/filter file that contains the corresponding prefixes with their maximum length and a list with the prefixes without maxlen to distinguish if the prefix belongs to CRXN or to dn42. The entitydb contains a bash script `build_maxlen_filter.sh` for this purpose. If you run this script with the argument `bird`, you will get a bird-compatible list with the maximum lengths. If you run the script with the `bird prefix-list` parameter, you will get a prefix list without the maximum lengths.
 
 ```
 define CRXN_IPs = [
-    include "<path-to-file>";
+    include "<path-to-file-1>";
+];
+
+define CRXN_MAXLEN = [
+    include "<path-to-file-2>";
 ];
 
 function is_crxn_net() {
   return net ~ CRXN_IPs;
 }
+
+function is_maxlen_valid() {
+  return net ~ CRXN_MAXLEN;
+}
 ```
-This bird configuration can be used to load the file. You have to replace `<path-to-file>` with the path of the filter file. The function `is_crxn_net` then checks whether a route complies with the rules or not.
+This bird configuration can be used to load the file. You have to replace `<path-to-file-1>` with the path of the filter file without maximum lengths and `<path-to-file-2>` with the path of the filter file with maximum lengths. Function `is_crxn_net` then checks if the prefix belongs to the CRXN network and function `is_maxlen_valid` then checks if the prefix is maxlen-valid.
 
 ```
-if (! is_crxn_net() ) then {
+if (is_crxn_net() && (! is_maxlen_valid())) then {
     print "[CRXN] Invalid crxn route: ", net;
     reject;
 }
 ```
-This configuration can then be added to your import filter before 'accept'. The line with `print` is optional. If you leave this line, every hjack attempt will be logged in the bird log output.
+This instruction checks whether a prefix belongs to the CRXN network and then whether the prefix is maxlen-valid. If it is not maxlen-valid, it is filtered and a message is issued.
+
+This configuration can then be added to your import filter before `accept`. The line with `print` is optional. If you leave this line, every hjack attempt will be logged in the bird log output.