Skip to main content

Network Access Layer Security

The campus access layer switching infrastructure must be resilient to attacks including direct, indirect, intentional, and unintentional types of attacks. In addition, they must offer protection to users and devices within the Layer 2 domain. The below terminology is Cisco specific, however similar features are available in products of other brands. 
The key measures for providing switching security on the access switches include the following:

Restrict broadcast domains
Spanning Tree Protocol (STP) Security
-       Rapid Per-VLAN Spanning Tree (Rapid PVST+)  (fast convergence)
-       BPDU Guard (shuts port down if a BPDU is received, prevents STP manipulation) 
-       Root Guard to protect against inadvertent loops (prevents other switches from becoming root bridge)
-       BPDU filter (stops BPDUs from being broadcast to access ports)
DHCP Protection
-       Implement DHCP snooping on access VLANs to protect against DHCP starvation and rogue DHCP server attacks
IP Spoofing Protection
-       Implement IP Source Guard on access ports to prevent IP spoofing
ARP Spoofing Protection
-       Implement dynamic ARP inspection (DAI) on access VLANs
MAC Flooding Protection
-       Enable Port Security on access ports (to limit number of MAC addresses allowed on a port)
Broadcast and Multicast Storm Protection
-       Enable storm control on access ports 
VLAN Best Common Practices
-       Restrict VLANs to a single switch (current design best practice, prevents STP issues)
-       Configure separate VLANs for voice and data
-       Configure all user-facing ports as non-trunking (DTP off)
-       Disable VLAN dynamic trunk negotiation on access ports (prevents VLAN hopping attacks)
-       Explicitly configure trunking on infrastructure ports rather than autonegotiation
-       Use VTP transparent mode
-       Disable unused ports and place in unused VLAN
-       Do not use VLAN 1 for anything
-       Configure native VLAN on trunk links to an unused VLAN (prevents VLAN hopping using double-tagged frames)

Source: Cisco SAFE Design Reference Guide


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

DNS response and error types

In this post we explore common DNS response codes. We will cover the following responses: NOERROR SERVFAIL NXDOMAIN NODATA REFUSED Throughout article we’ll refer to the following RFCs: RFC 1034 - DOMAIN NAMES - CONCEPTS AND FACILITIES RFC 2308 - Negative Caching of DNS Queries (DNS NCACHE) RFC 2136 - Dynamic Updates in the Domain Name System (DNS UPDATE) RFC 8914 - Extended DNS Errors Response Codes - RCODEs The DNS RCODES are best defined in RFC2316 .  They signify what type of response was sent by the server. “RCODE   Response code - this four bit field is undefined in requests and set in responses.”   The table below shows the summary of the currently defined RCODEs. Mnemonic Val Description NOERROR 0 No error condition.

DNS blocking in Indonesia

DNS based censorship and domain blocking in Indonesia is very inconsistent among ISPs. There’s a government mandated black list which the ISPs operating in the country should enforce. However, Indonesia lacks centralised internet infrastructure and has many separate ISPs. In addition, the Indonesian government granted ISPs the authority to block content at their own discretion. All of this leads to a very inconsistent DNS blocking in Indonesia. Official DNS domain blacklist in Indonesia The Government mandated DNS blacklist is published in a redacted form and can be downloaded here: . This is where the blocked domains get redirected to. We can search the database and check if a domain is blocked. In the screenshot below we can see that a popular cryptocurrency exchange is blocked (Ada) and that is not (Tidak Ada) - thanks to Google Translate. Examples of blocked DNS queries dig @ ;; global options: +cmd ;; Got