Skip to main content

BGP Best Path Selection Algorithm


  • Check if the next-hop is reachable. If yes, then proceed
  • The path which has the highest WEIGHT
  • The path which has the highest LOCAL_PREF
  • The path which has been locally originated via a “network” or “aggregate” BGP command or through redistribution from an IGP
  • The path which has the shortest AS_PATH
  • The path which has the lowest origin type
  • The path which has the lowest MED
  • EBGP is preferred over IBGP
  • Prefer the path which has lowest IGP metric to the BGP next hop
  • Determine if multiple paths require installation in the routing table for “BGP multipath”
    In case both the paths are external, prefer the path which was received first (the oldest one)
  • Prefer the route which comes from the BGP router with the lowest router ID
    If the originator or router ID is the same for multiple paths, prefer the path which has minimum cluster list length. (This is only present in BGP RR environments. It allows clients to peer with RRs or clients in other clusters. In this scenario, the client must be aware of the RR-specific BGP attribute.)
  • Prefer the path which comes from the lowest neighbor address.

Labels:

Comments

Post a Comment

Popular posts from this blog

MITRE ATT&CK - Kerberos Vulnerabilities and Security

From the previous post, the summary of Kerberos authentication process is as below: For the initial authentication, the user’s client machine sends a request to the KDC  Authentication Service (AS) . The request includes details like the user’s username, and the date and time. All information except the username is encrypted using the hash of the user’s password. The KDC AS uses the username to look up its copy of the user’s password hash and uses it to decrypt the rest of the request. If the decryption is successful, that means the client used the correct password hash and the user has successfully authenticated. Once the user is authenticated, the KDC AS sends the user’s client a  ticket granting ticket   (TGT) . The TGT includes a unique session key and a timestamp that specifies how long that session is valid (normally 8 or 10 hours). Importantly, before sending the TGT, the KDC encrypts it using the password hash for a special account, the  KRBTGT account. ...
4 comments
Read more

Checkpoint - Exporting Objects in CSV format

Be it a Network Operations Manager, Security Architect or a Security Auditor, the people up the hierarchy always harangue the Security Engineers to compile the list of firewall objects or rules or policies or the traffic statistics and so on.. This can turn out to be quite hectic especially if there are no built in features to systematically provide the output in a "layman-readable" format. Come, Checkpoint's "Object Explorer..."  which not only provides the output in the "layman-readable" format, but also provides in-built filtering mechanisms, thereby ensuring that the Security Engineer doesn't have to rely on Google for building his scarce Microsoft Excel data filtering skills. The following screenshots will show how easy it is, with Checkpoint R80.10 to generate the firewall configuration inventory. On the SmartConsole Unified Portal, navigate to Menu >> Open Object Explorer... Select the Categories you wish to see in your output: Click o...
Post a Comment
Read more

MITRE ATT&CK - Understanding Kerberos (for Golden Ticket Attack)

Kerberos = Network Authentication Protocol used by AD environments Provides authentication by issuing tickets to authenticate users and allow them access to the services Tickets are distibuted by KDC (Key Distribution Center), which is typically a Domain Controller (DC) During initial authentication, a TGT (Ticket Granting Ticket) is a ticket asigned to a user by KDC. TGT is later used to authenticate the user to the KDC in order to request a service ticket from TGS (Ticket Granting Service). Service tickets are granted for authentication against services. List of steps / negotiations for Kerberos authentication (of the user with the service): The user requests  (AS-REQ)  a TGT from the KDC and the KDC verifies and validates the credentials and user information. This request if often done automatically at login. After authenticating the user, the KDC sends an encrypted TGT back to the requester  (AS-REP) . The user presents the TGT to the DC and requests a TGS  (TGS-...
Post a Comment
Read more