Skip to main content

Network Distribution Layer Security


Distribution layer aggregates access layer switches. This is where all packet manipulation that hasn’t already been performed in access layer should take place. I’m focusing here on infrastructure protection rather than device hardening. Everything below is of little benefit if default passwords are used! Even though, properly configured ACLs restricting access to management interfaces would in some cases effectively prevent an attacker from being able to login to a switch. Hardening is essential. This is what we call defence in depth.

-          Routing infrastructure protection

o     Authenticate routing neighbours with MD5 (prevents rouge routing info injection and routing table manipulation)

o    implement route filtering (as above)

o    use default passive interfaces (tells an interface not to listen to or distribute routing protocols, this prevents infection and interception of routing data, furthermore it makes determining what routing protocol is in use more difficult)

o    log neighbour changes

-          Implement redundancy (good, resilient design is the key)

-          Implement ACLs (Network segmentation is implemented here, I.E. preventing finance VLANS access to HR servers)

-          Implement Infrastructure ACLs (or iACLs as Cisco calls them) to restrict access to infrastructure management IP addresses (be careful not to block transit traffic but only traffic aimed at Core or distribution devices / VLANS itself)

NOTE: iACLs are only applicable in the distribution layer of a multi-tier design where the routed edge interface is on the distribution switches. In a routed access design, this is enabled in the access layer.

-          Apply uRPF to block packets with spoofed IP addresses (Unicast Reverse Path Forwarding – the router will check if the source IP is reachable before forwarding a packet, the same can be accomplished using ACL that allow traffic only from subnets that exist in particular network segment)

NOTE: uRPF is only applicable in the distribution layer of a multi-tier design where the routed edge interface is on the distribution switches. In a routed access design, this is enabled in the access layer. 

Comments

Popular posts from this blog

x.509 Certificates - Critical vs non-critical extensions

Extensions are used to associate additional information with the user or the key.  Each certificate extension has three attributes - extnID, critical, extnValue extnID - Extension ID - an OID that specifies the format and definitions of the extension critical - Critical flag - Boolean value extnValue - Extension value  Criticality flag specifies whether the information in an extension is important. If an application doesn't recognize the extension marked as critical, the certificate cannot be accepted. If an extension is not marked as critical (critical value False) it can be ignored by an application. In Windows, critical extensions are marked with a yellow exclamation mark,  View certificate extensions using OpenSSL: # openssl x509 -inform pem -in cert.pem -text -noout (output abbreviated)         X509v3 extensions:             X509v3 Key Usage: critical                 Digital Signature, Key Encipherment             X509v3 Subject Key Identifier

Count number of lines - 'findstr'

How do I count number of lines in a command output? findstr /r/n "^" | find /c ":" Above commands will display number of lines output by whatever command (well, nearly whatever) you specify in the front.  For example:  C:\>ping localhost | findstr /r/n "^" | find /c ":" FINDSTR: // ignored 12 This comes handy if you want to find out how many OUs you have in Active Directory: dsquery ou  -limit 0 | findstr /r/n "^" | find /c ":" How many user accounts there are: dsquery user -limit 0 | findstr /r/n "^" | find /c ":" Computers: dsquery computer -limit | findstr /r/n "^" | find /c ":"

Cisco ASA Certificate Revocation Checking

ASA supports status verification using CRLs and OCSP. CRL can be retrieved using HTTP, LDAP or SCEP. Revocation checking using CRL: Over HTTP: ciscoasa(config)# crypto ca trustpoint ASDM_TrustPoint2 ciscoasa(config-ca-trustpoint)# revocation-check crl ciscoasa(config-ca-crl)# protocol http By default ASA will use address listed in CDP extension of the certificate that is being validated.  To override default behaviour we need to add the following in the CRL configuration context. ciscoasa(config-ca-crl)# policy static ciscoasa(config-ca-crl)# url 1 http://cdpurl.kp.local/crl.crl Over LDAP: Certificate I'm using for this lab, doesn't have LDAP address in its CDP extension. Therefore I'm using "policy static"  to specify LDAP URL where CRL can be retrieved.  ciscoasa(config)# crypto ca trustpoint ASDM_TrustPoint2 ciscoasa(config-ca-trustpoint)# revocation-check crl ciscoasa(config-ca-trustpoint)# crl configure ciscoasa